Major Comp issues

I need some help. My computer is having some issues which really annoy me.
Randomly, the sound will stop working and when I bring up iTunes, it gives me an error and the only way to fix it is a reboot.

Among some other problems are: It's VERY slow. It has issues burning cds/dvds sometimes. Software frequently won't load. Firefox crashes ALL the time. Rhapsody does too. The internet goes out all too often (we have a Netgear WGR614v6 router and a Westell Wirespeed B90-210030 modem/router). It's also slow. We have DSL lite, but it's not usually this bad.

We have a 2.93ghz processor and 1gb of RAM. We run XP Pro SP1. I can't upgrade to SP2 or 3 because of administrator issues (the person, not the account). I run a Checkdisk weekly, as well as a defrag and disk cleanup (I use Smart Defrag and CCleaner). I have.......4 anti-spyware programs and Malwarebytes. I have ZoneAlarm free and Avast! 4 Home. How the bloody heck do I fix this thing?!?!?! Can someone help?