but how much can windows xp home cost ? like 20?

Try $100
When it was first released Home edition retailed for $199.00
Pro was $299.00
What you pay for is the license to use it-- and at first release ... even tech-support from Microsoft.
When you buy it with a PC... it is licensed for that PC and ONLY that PC. Of course this is very much a grey-area legally-- because a PC has many parts. Usually when you change a couple of major components like mobo/Video-card the activation when you reinstall won't work-- you have to actually call Microsoft... they ask you a couple of BS questions --and give you a new activation code.
This is why we've been trying to bring this item to your attention-- nothing's as simple as it looks

BuyCheapSoftware.com: Discount Microsoft software for Home and Business

oh, and i just realized, the systemax does come with OS.

Here is a deal for windows xp pro os

For an extra charge- add $99 I believe. Not installed-- but that's good. If they install they usually add all manner of junk to it.

Your ram won't work if you buy a brand new motherboard. Also I didn't look too closely but if your hard/cd/dvd drives are all IDE then you could have trouble transferring it all to a new motherboard as most of them are using SATA now with maybe 1 IDE slot. If not then you'll want to buy a new HD/windows pack

It's really not as hard as people make it out to be. Check out Newegg.com - Computer Parts, PC Components, Laptop Computers, Digital Cameras and more!. Alot of times they'll sell components in packages with discounts.

What you will have to buy:
CPU processor
Motherboard
Ram
Power supply- sometimes it might not be needed but usually when you upgrade an older computer, the older power supply won't crank out enough power for the new components.

some stuff I just looked up really quick. Total=$849.94 w/o shipping.
Newegg.com - ASUS P5W DH DELUXE/WIFI-AP LGA 775 Intel 975X ATX Intel Motherboard - Retail
Motherboard. Has 2 sata and 2 IDE connectors to make sure your current stuff will work while leaving room for you to upgrade to SATA if you want. Also has room for alot of RAM and plenty of PCI ability

Newegg.com - Rosewill RX850-D-B ATX12V v2.2 & EPS12V v2.91 850W Power Supply 100 - 240 V TUV, FCC, UL, CE, ROHS - Retail
Newegg.com - Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache LGA 775 Processor - Retail
Cpu and Psu comboed togeather. Very fast cpu and the psu should have enough power for whatever you want to do.

Newegg.com - G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
good RAM. Might want to go with some better stuff if you want to overclock though.

You can re-use your current video card if you want. It's not the best but if you're not really into gaming it doesn't matter much.

Newegg.com - Western Digital Caviar RE WD3200YS 320GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM
big sata hard drive.

Newegg.com - Microsoft Windows XP Media Center Edition 2005 w/SP2B - OEM
xp media center. You can go vista too, home premium is about the same. Just seems like there's less problems with xp.

Also I'm not sure if your current case is a smaller case. If you don't have a full or mid tower then you might have to shell out another 50-100 bucks for a case.

There you go. That system will be up-to-par for years to come. I'm sure you could find better systems pre-built... but they'll be waaaaay over that price.

Really building it isn't that hard. Just make sure you ground yourself to the case(touch it) while you're installing the motherboard and everything. Really the biggest set-back you'll run into is if you get a defective part.

thanks everyone! do you guys think these online stores "tigerdirect , newegg" will participate in "black friday"? if, so ill just keep saving and wait