My computer reboots whenever it feels like it...
What is causes that?

Consult you computer hardware vendor since this problem of reboot without any reason occurs if there is a problem with your RAM.

It was home built about 1 yr ago...

What happens is that when Im on the computer doing anything, all of a sudden it REBOOTS on me...

I have a SOYO DRAGON+ Mobo...

Please check the RAM slot might not proplerly be fixed and also check the virtual memory.

RAM is in fine...

What should the virtual memory be like

I have the same prob, esp. since you built it. SOYO mobo is kind of of cheap and after 1 yr or so tends to get bad.
Most reboots happen because your power supply is bad, too. The power good line of the power supply may not be receiving enough voltage. If you are sure your RAM is good (same PC bus, trying different slots,etc.), check all the other basics,like IRQ,jumpers,bios updates, and any loose cards, esp. video card. Also try placing your sound and video cards 1 slot apart from each other.
This sometimes help. If none of this helps, the prob may also be with the mobo hard drive controller. Some hard drive vendor such as Western Digital has a floppy disk or download from their website you can run to test if the controller is indeed bad. In that case, replace with another good mobo like TYAN.