the program which you use is called "resize2fs" but you must first make your partition bigger using fdisk.
Using fdisk (or cfdisk i guess) delete the partition, then remake the partition (starting at the same spot) ending later on the harddrive. Then fdisk will show you how many blocks it is i think.
Then use resize2fs to resize the filesystem to that size. check the man page for resize2fs "man resize2fs"
edit: that was assuming you are making it bigger... its a little different if you want to make it smaller.
[ February 27, 2003: Message edited by: The Master of Reality / Bob ]