I originally installed Zipslack, then copied everything to an ext2 partiton. Unfortunately, this partition filled up pretty quick, so I decided to use Parted to resize my partitions. I originally wanted to shrink the Windows partiton and expand the ext2 partiton, but Parted kept telling me that the ext2 partiton had unsupported features. I shrunk the Windows partition, deleted the ext2 one, copied the iso to cd, and reinstalled slackware into a new larger partiton. Unfortunately after reinstallation the keyboard started acting up in X. It would sometimes type more letters than I intended and would "lock" on a key if it was held down for a few seconds (i.e. if I held down the "w" key for a few seconds it would type w's until I pressed it again). Also while typing the mouse would occasionally jump to the bottom of the screen. These problems would also spread to consoles that weren't using X. How can I fix this?

I've never seen that. Maybe have a look in /etc/X11/XF86Config and see if your:
# Core keyboard's InputDevice section
# Core Pointer's InputDevice section

Is all in order?
Maybe run /etc/X11/bin/xf86config again?
Is your mouse set to /dev/psaux ?

Option "Protocol" "IMPS/2"
Option "Device" "/dev/psaux"

My mouse has been set as "/dev/mouse" in both installations.
As for using xf86config, I don't like it because it takes a while and overwrites the old file (I'd have to add entries for my scrollmouse all over again).
I'll try to post my XF86Config.

I used xf86config to make a new XF86Config file, and the keyboard problems seem to have gone away. However, the mouse still jumps to the edges of the screen while I'm typing.
My /dev/mouse is linked to /dev/psaux, and the protocol is IMPS2.

That's a USB mouse?

No, it's ps/2

Option "Protocol" "PS/2"