Welcome to the Forums.
I am exceptionally glad to let you know that the Abit KT7A is a great motherboard for overclocking and has recieved outstanding reviews and is widely used in these forums, some people appear to have a few problems with this motherboard however I have none even though I have built four machines using it.
Most of the problems seem to generally surround the soundblaster live cards however the advice of these forums can help you cure most things, all I would suggest as advice is read the manual carefully and ask for help if and when you need it.
If you are on a tight budget, perhaps you should consider a AMD Duron as these perform exceptionally well and are reasonably priced, I have a Duron 800 @ 1050 mhz. If you can stretch your cash a little bit further then a Athlon 1 ghz would be better.
Ensure that you have good cooling, do not cut corners on this to save money, get a reputable heatsink fan like a FOP 32 or FOP 38 and not an ORB.
Cases are a personal matter and I like full towers due the generally better airflow, I dont have a branded quality case and just found something that suited my needs, ensure though that the case has a quality 300 w power supply.
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Duron 800 @ 1050 with Global Win FOP-32 (140 x 7.5)
Abit KT7A-Raid
512 mb (PC133 Crucial Stuff CAS 2)
Hard Drive Cooler
Elsa Eraser X2 Gforce with Blue Orb
modified to display as a Quadro and overclocked
Sound Blaster Live
Full Tower with 5 (120 mm) case fans with seperate PSU