kristofer - welcome to SPCR !
> What kind of voltage do you guys recommend for a XP 2000 TB?
rule of thumb - you can easily lower voltage by 0,5V (stock settings), if you underclock (say 1600+) you can lower voltage to 1,475V
> And if I lower the voltage too much (by modding) I fear that
> my computer won't start up anymore.
make sure that your mobo bios allows OVERVOLTING, because if you permanently mod your cpu (1,475V) you can always OVERVOLT in bios to have 1,6V or 1,5 if your computer hangs at low Vcore voltage. It's good to have backup CPU (anything that fit into mobo) in case your computer won't even boot to bios - in that case you can put backup cpu (it can be your friend's cpu
- it is 100% safe operation), enter bios and make some changes (lower FSB, rise Vcore) and than insert your cpu again.
If you don't have spare CPU, try to set max OVERVOLT and lowest FSB (ie 66Mhz) as bios defaults - some bioses have option to save current settings as bios defaults (or you can mod your bios BIN file and flash it). In that case - when you reset your bios settings (via mobo jumper) you can likely boot with your 1,475V moded cpu, because it will be running on max OVERVOLT (close to its standard voltage) and with lowest FSB.