personally i don't see any point to upgrading your motherboard "just because you've had it a few years". if you need a new feature or wish to upgrade your whole pc go ahead
but don't upgrade the motherboard just for the sake of it.
you could get a new motherboard and use your current hardware but it wouldn't give you any extra power and you'll have to get it second hand as all manufacturers have discontinued socket 370 motherboards (the kind which your motherboard is).
if you wish to get an entirely new pc then it will really help if you give us an indication of your budget. i think you should look into a Core 2 Duo e6600, a decent mid range LGA775 motherboard, 1-2GB of DDR2 memory (2GB if you game or do any intensive work like video encoding/editing) and a PCI-E video card of your choice (no lower than a 7600GT or X1800 if you game a lot)