what's your mobo? make sure that the mobo supports what you buy esp RAM, processors, High end HDD (my old pc never suppoorted hdd>32gb)
P3 800MHz-- your mobo may not support processor more than 1ghz! so there's no point upgrading the processor(oonly 200mhz diff)
256MB Ram.. most probably it's a SD ram... after the ddr came into the market the SDRAM has been going thru a slow death.. ppl hardly use them.. but keep searching(i wish we had the bazzar section up!!)..
VIA 601 BS4 (8 MB Video Card)
No AGP Slot
that's a prob!!--- PCI graphics were no where near the AGP ones.. so no place for them in the market too... and now this PCIe!! .. this PCI graphics card may cost you a bit on the heigher side(if you were lucky to find one)