What website are you buying from. Availablity will affect what you get, so we should know what options you have at your preferred site.
I've heard of ncix.com, and they're rated well.
http://www.resellerratings.com/seller2064.html
tigerdirect.ca, would probably be my second choice.
Also, what does $700 include. Is that for just a mobo, cpu, ram, and video card, and case/psu or do you need a monitor speakers, xp, mouse, keyboard, hd, dvd drive, etc too? Some people only include the hardware in the case(cpu, mobo, ram, video, hd, dvd drive, psu, case, fans/heatsink, cables, not including xp) when they say $700, and other people say $700 and they mean that for the case and everything in it +xp, +lcd/crt monitor, +mouse/key, +speakers, etc. Oh, yeah, does the price include shipping/tax or not?
Also, how good of performance do you want as far as graphics are concerned? Do you want to play the newest games(or think you ever may want to)?
Here's a rough sketch for you from ncix. It'll probably need changed to fit your needs, but it's a start.
So far a asus a8n-e sounds good to me.$168
http://www.ncix.com/products/index.php?sku=14268&vpn=A8N-E&manufacture=ASUS
And a 3000+ 939 cpu$215
http://www.ncix.com/products/index.php?sku=14415&vpn=ADA3000BPBOX&manufacture=AMD
And a gig of pc3200 ram(corsair, ocz, crucial, kingston, etc are all good).$138
http://www.ncix.com/products/index.php?sku=9821&vpn=VS1GBKIT400&manufacture=CORSAIR
A antec 1650b case(it's cheap and seems ok).$80
http://www.ncix.com/products/index.php?sku=12887&vpn=SLK1650B&manufacture=ANTEC
x600pro(mid range card)$126
http://www.ncix.com/products/index.php?sku=12682&vpn=S-X600-128&manufacture=SAPPHIRE
dvd $30
http://www.ncix.com/products/index.php?sku=8984&vpn=GDR-8163B-BLACK&manufacture=LG Electronics
80gb hd$82
http://www.ncix.com/products/index.php?sku=6470&vpn=ST380011A&manufacture=Seagate
Total = ~$840, so it's overbudget, and that doesn't include tax, shipping, or xp, monitor, mouse/key, etc.
xp $118
http://www.ncix.com/products/index.php?sku=6526&vpn=N09-011520OEM&manufacture=Microsoft
If you'd use a mobo that's cheaper, like this.
http://www.ncix.com/products/index.php?sku=13861&vpn=VNF4 ULTRA&manufacture=CHAINTECH COMPUTER
512mb of ram, and a case that costs about half as much, it'd bring the total to about $729.
It's hard to build a decent computer for $700 us, but canadian is even harder.