LinuxQuestions.org - help with long delayed system updates(?)

Hi folks, I wonder if anyone can give me a helping hand...
I have a webserver that hosts numerous websites, but which I haven't touched for about a year and a half (mainly coz my partner was very ill and I was just doing the minimum essential work to keep my head above water).
I am thinking now of just doing an apt-get upgrade, but the longer it got left, the more scared I got that it has been so long that everything will break, and the server will stop working... eek! I am not bothered about keeping abreast of the latest kernel etc (all though I spose I should eventually be?) - I just feel that I might be leaving my machine vulnerable.

I spose generally - How much should I do? or should I just leave it alone? (if it ain't bust, don't fix it)

If I were to just do an apt-get upgrade, am I worrying unnecessarily? or is it likely to go wrong? anything I should watch out for in particular? can anyone help me out if it all goes pear-shaped?

I am not exactly a newbie, but I don't spend much time doing this stuff, and Im fairly new to debian (so please treat me as such).

Thanks in advance for any input :-)...

Some things to know (if you are willing to help), is that:

The machine is just running apache, php module and cli, mysql and mail, and is remotely managed via ssh (no xwindows or anything for local usage)

/etc/debian_version reads 3.0 (but this has been manually altered to force something to work in the past, and I am not sure if it is correct - does any installation software actually use this? or is it irrelevant and just for our eyes?)

Kernel is 2.4.24

my sources.list is:

deb ftp://ftp.debian.org/debian sarge main contrib
deb http://www.backports.org/debian stable cyrus-sasl2
deb http://debian.blueyonder.co.uk/ testing main
deb http://security.debian.org/ stable/updates main contrib

(I don't know how this list got compiled, or if it covers all the necessary bits. NB I am in the UK).

when I do an apt-get -u upgrade
it gives me...

<snip>
Reading Package Lists... Done
Building Dependency Tree... Done
The following packages have been kept back:
apache apache-common apache-utils base-config bind9 bind9-host console-common cpp discover dnsutils g++ gcc gnupg
libapache-mod-ssl libdbd-mysql-perl libdbi-perl libdiscover1 libisc7 libisccc0 libisccfg0 libldap2 libmime-perl libnewt0.51
libopencdk8 libxslt1 libxslt1.1 lilo lwresd lynx mutt php4 postfix postfix-tls python-newt python2.3 spamassassin tasksel
whiptail
The following packages will be upgraded:
adduser analog apache-doc apt apt-utils aptitude ash at base-files base-passwd bash bc bin86 bind9-doc binutils bison
bsdmainutils bsdutils bzip2 console-data console-tools coreutils courier-authdaemon courier-base courier-imap courier-pop cpio
cpp-3.3 cramfsprogs cron dash dc debconf debconf-i18n debianutils defoma devfsd dhcp-client dictionaries-common diff
discover-data doc-debian doc-linux-text dosfstools dpkg dpkg-dev dselect e2fslibs e2fsprogs efibootmgr eject elilo fakeroot
fdutils fetchmail file findutils finger flex fontconfig ftp g++-3.3 gcc-3.3 gcc-3.3-base gdb gettext-base grep groff-base gzip
ifupdown info initrd-tools initscripts iptables kernel-package klogd less libacl1 libapache-mod-ssl-doc libasn1-6-heimdal
libattr1 libblkid1 libbz2-1.0 libcap1 libcomerr2 libconsole libcurl3 libdb2 libdb3 libdb3-util libdb4.1 libdb4.2 libedit2
libexpat1 libfam0c102 libfontconfig1 libfreetype6 libgc1 libgcc1 libgd2-xpm libgpg-error0 libgpmg1 libgssapi1-heimdal
libhtml-parser-perl libhtml-tagset-perl libice6 libident libidn11 libio-stringy-perl libjpeg62 libkrb-1-kerberos4kth
libkrb5-17-heimdal libkrb53 liblocale-gettext-perl liblockfile1 libltdl3 liblwres1 liblzo1 libmagic1 libmcrypt4 libmm13
libmysqlclient10 libmysqlclient12 libncurses5 libncurses5-dev libncursesw5 libnss-db libpam-modules libpam-runtime libpam0g
libpcap0.7 libpcre3 libpng10-0 libpng2 libpopt0 libreadline4 libroken16-kerberos4kth libsasl2 libsasl2-modules
libsigc++-1.2-5c102 libsm6 libss2 libssl0.9.6 libssl0.9.7 libstdc++2.10-glibc2.2 libstdc++5 libstdc++5-3.3-dev libtasn1-0
libtext-charwidth-perl libtext-iconv-perl libtext-wrapi18n-perl libtimedate-perl libunicode-string-perl libuuid1 libwrap0
libx11-6 libxext6 libxft1 libxi6 libxml2 libxmu6 libxmuu1 libxp6 libxpm4 libxrandr2 libxrender1 libxt6 libxtrap6 libxtst6
libzzip-0-12 linux-kernel-headers login logrotate lsof m4 mailagent mailx make makedev man-db manpages manpages-dev mbr mdadm
mime-support mlock modconf modutils mount mtools mtr-tiny mysql-client mysql-common mysql-server nano ncftp ncurses-base
ncurses-bin ncurses-term net-tools netbase netkit-inetd nmap nvi openssl passwd patch pciutils perl perl-base perl-modules
php4-cli php4-common php4-gd php4-mysql popularity-contest procmail procps proftpd proftpd-common psmisc python quota quotatool
raidtools2 rcs rdate reportbug rsync sasl2-bin setserial sharutils slang1 slang1a-utf8 spamc ssh strace sysklogd syslinux
sysv-rc sysvinit tar tcpd tcsh telnet texinfo time traceroute ucf unzip util-linux w3m wget whois xfree86-common xlibs
xlibs-data zip zlib1g
259 upgraded, 0 newly installed, 0 to remove and 38 not upgraded.
Need to get 94.4MB of archives.
After unpacking 19.7MB of additional disk space will be used.
Do you want to continue? [Y/n]
</snip>

apt-get -u dist-upgrade
....gives me:
<snip>
The following packages will be REMOVED:
postfix-tls
The following NEW packages will be installed:
apache2-utils cpp-4.0 dmidecode g++-4.0 gcc-4.0 gcc-4.0-base laptop-detect libapache-mod-php4 libapr0 libbind9-0
libconvert-binhex-perl libdb4.3 libdevmapper1.01 libdigest-sha1-perl libdns16 libdns20 libgcrypt11 libgnutls11 libisc9
libisccfg1 libmysqlclient14 libnet-daemon-perl libplrpc-perl libreadline5 libslang2 libstdc++6 libstdc++6-4.0-dev libtasn1-2
libusb-0.1-4 lsb-base
The following packages have been kept back:
discover libdiscover1
...</snip