Sorry just joined, but I tend to agree with the others on building your own computer.  Anything that you throw together would be better then the Emachine you have.  Though if you plan to work with graphics I would suggest more than a Gig or ram.  If you do serrious graphics even if just for fun, get as much ram as you can affrod.  If you build your own make sure you get an Motherboard with at least 4 slots of ram then try to put twins into those slots.  As long as you pair the memory up you will get far more power out of them then miss matching.  By having 4 slots for ram you can get cheap 2gig twins Thats 1+1gig.  This way you can add another set of memory when you save another 40 (give or take a couple   US Dollars)   By building your own you get what you want and you can shop for bargains.  WD drives are good, Though I have a problem with sea gate or fuji.  Don't let anyone talk you into getting a Mother board with the graphic's card built in.  they cost more and wear out much faster.  

Duel core processers are inexpensive now, A processor and MB can be bought for under a hundred.  The last time I price the Pair it was 78 dollars for a decent AMD.

It could be the power supply as some one suggested though it sounds like the mother board to me.  Being an Emachine they don't use quality parts.   Just adding you own HD to it yourself says you can build one.   I'm sure there are plenny of people here willing to walk you though the process through MSN or Yahoo.  It can be intimitading, but very rewarding.  By doing it yourself you will never be done upgrading.  Also I do Agree stick with XP as long as possible, and by the way on the back of your emachine or the bottom you will see the autherization for the xp on it.  Copy this number as it is you ticket to legally borrow a copy of xp to put back on your new computor.  Most repairman won't tell you this.  Some will reinstall XP and charge as though it was a new copy.    You paid for it, so its yours.