Repair/Reinstall XP SP-2

My PC has a 3.06 GHz P4 with 1 GB of RAM running Win XP Pro 2002 SP2 on my
main 200 GB hard drive.

For a long time (until last week), I had so many video files on my main hard
drive that the free space averaged only about 7 GB, and sometimes my
downloads stopped because my main 200 GB hard drive was completely full.

My PC shipped with SP1, and I installed SP2 from the CD at the beginning of
2006.

After installing SP2, I tried to upgrade my Creative Audigy 2 software,
which repeatedly caused my PC to hang with a blue screen. Sometimes I had to
use System Restore, and my sound card hasn't worked properly since then.

I used to run Windows Error-checking and Windows Defragmentation
periodically, but after the problem with the Audigy 2 software, my PC would
hang with a blue screen at the end of Error-checking. I haven't run
Error-checking and Defragmentation since then.

For the past several months, my PC has been very sluggish.

I am running Zone Alarm 6.5.737 firewall, anti-virus, and anti-spam. I was
running Webroot Spy Sweeper, but I disabled it out of concern that it might
be a problem (as Spy Doctor was).

Last week, I moved my video files to DVD+R disks, so I now have 140 GB of
free space on my hard drive. This week, my PC has been significantly faster,
although it still seems sluggish.

I think I may have damaged XP SP2 with my Audigy 2 troubles, and I would
like to repair or reinstall XP SP2.

I would prefer to repair XP SP2, because I assume that reinstalling XP SP2
would require me to reinstall all my other software.

After repairing or reinstalling XP SP2, I would like to try to install
Audigy 2 again.

In case this affects what you recommend, I have the SP2 CD, and my PC has a
second 200 GB hard drive that is identical to the main one.

What is the best thing to do?

Thanks.