I have installed redhat 7.2 as a dual-boot with win 98. Does anybody know how to increase the size of existing linux partition? ( Or shall I have to re-install it again ???? )

Also can anyone suggest a method to access the files in the windows partition from linux and vice versa?????

You can use parted (it is included in RH, but it may be not installed in your system, just find parted RPM and install it. My guess: 1st installation cd).
You can access Windows partitions (NTFS: read only). It's build in your kernel (if you're using the one that comes with your distro). Do you have /mnt/windows or a similar directory? Windows partition contents should be inside. If not, try to mount it manually
mkdir /mnt/windows
mount -t vfat /dev/hda1 /mnt/windows
I assume you have Windows installed on first partition of first hard disk and it's using FAT32 (if not, change the values). If it works you can add an entry to fstab.
From the Windows side you can use a program like Explore2fs (http://freshmeat.net/redir/explore2f...explore2fs.htm).

Ok ! Now one more Q. How can I use parted safely i.e without doing any harm to the windows partition?

Well you should always back up your data just incase

Garry