i'm wondering if you can actually upgrade the Emachine e4026's cpu and if so do i need to re install windows afterwards as i don't have a disk. i would also like to know what would be a good upgrade i was thinking a pentium dual core 2ghz instead of a single core 2.9ghz
The problem with this old system is that even if it allows you to upgrade the performance that you can get from it is going to be very limited. You might be able to use an Intel® Pentium® D and Intel Pentium 4 processor in socket 775. When we moved to the Intel Core® 2 Duo processors the older processors llike the ones that this board would upgrade would allow you to use have all been discontinued. So finding a processor sill come harder.
I beleive thats a 915g chipset system which only support pentium 4 cpu's. So you might be able to find a P4-670 or 672 (3.8ghz) and run that. I wasnt able to verify that your motherbd supports those cpu's ( the chipset does) so please google for it before you buy one and definitely update your bios before the upgrade.
Personally, I wouldnt bother upgrading that old system. your money is better spent in upgrading the motherbd, cpu, & ram to something much newer.