why need 3 partitions?
 

what is the advantage of having a /, /home and swap? why not just / and swap? the only reason i can think of is over fragmentation issues, is there any advantage to having more partitions?

because you can then do things such as installing multiple distributions that all use teh same home directory. Also you can then reinstall linux without erasing your own home data. there are many otehr advantages of splitting up file systems. /usr and /tmp and /var are all pretty common two. makes the system more secure. mainly in areas of being a big server and such though, where space is not an issue, and are not always relevant for home users

you can run more than 1 distro at a time? cool :)

what goes in the var directory anyway? i haven't found a use for it yet.

There can be more than one reson for that.
when you try to install linux after the 1024 cylinder limit it gives you error, to over come that you can create a third partition, say /boot of 50 mb, that will solve the problem

well.. used to. it's irrelevant now.

oh ok

One reason for multiple partitions, especially for /var, is in the event a process goes haywire and starts filling up a log file. If the var partition becomes full, in it's own partition, it will not effect your ability in correcting the problem or rebooting. If / was full, you'd have some major problems. THe same can be said for /tmp.

With the advent of JFS and LVM etc, filesystem management becomes easier with multiples. -mk

heh, didn't mean to defalte you.. yeah that's certainly one of the main reasons for a /boot, and there are similar advantages for keeping it, generally tho it'll hang around in conventions a fair while tho, simply becasue it used to be an issue ( i dare say that some distros do still suffer from it.. prolly slack 8.0, but then 8.1 is out soon)

/boot is nice to have your primary boot partition, and if anything goes wrong with it you can just boot from floppy and your sys is intact.
also
/var and /tmp are really usefull for hdd conservation. having a linux server writing logs, mail... all the time, easily causing bad blocks on hdd, and having those partitions at the end of hard disk is a smart idea, since you can just make new partition in front and forget about bad blocks at the end of drive.

I'm all over keeping /home it's own partition. Multiple distributions sharing home. If you reinstall, change distributions, whatever you can save your home partition.

In my early Linux days I clobbered home a time or two before catching on ;)

as for sizes of partitons......should / be a % of the hard drive or should it be a set number?

if i had an 80gb hard drive, would the / directory be only 10gb and /home be like 70?

so, if you opt for the layout you presented it is perfectly fine, exept if you gonna load lots of applications they will all reside under /usr or /opt which as you present will be under / , and hence, they will require space. If it was in my case I'd rather do at least 5 partitions,
/ - 200 Mb,
/home > 50 G
/usr >20
/tmp - 2G
the rest I'd dedicate to /var, /opt etc.

yeah, your / directory should never have to be over a gig in most cases if you setup more than just /boot, swap and /.
with an 80 gig drive you could do something like this:

/boot = 64 megs
swap = no more than 200 megs
/ = no more than 1 gig
/usr = 5 to 10 or more gig's
/var = around a gig
/tmp = same as /var
/home = maybe the rest of the drive

so the bad boys are home and usr huh? k :)

i'll stick to just / and /home then.......the more intricate i try to set something i don't know, the more screwed up it is.