I strongly recommend you go with a Core 2 processor, even a Core 2 Solo.  The big difference is a much improved instruction set - my previous machine was a Pentium 4 dual core 3.8 gigahertz, and my current machine is a Core 2 Extreme quad core 2.66 gigahertz, and even for single-threaded tasks (things that only run on one core) it is noticeably much faster.

I urge you to be more specific about the graphics card.  If you give them that much leeway you're going to end up with a low end card that won't cost a whole lot less money, but will perform significantly slower in the viewport.  No comment on ATI but if you choose Nvidia, try to stick with 7800 or 7950 based cards.

The prices on all the desktops on your link seem quite high and specs are quite low.  I can't recommend any of those as a starting point.

Can I ask for what reason you want your hard disk split up into three partitions?  There used to be technical reasons why that was useful but now it really doesn't help, unless it's just to help you keep your stuff organized.  You can run into trouble if you fill up a disk partition and then you're kind of stuck, because resizing partitions with a lot of data on them can be pretty difficult.  You might want to just consider one large partition with your data stored in subdirectories.

Currently looking at some prices on shopbot.ca for all-Canada vendors, I can offer a similar list of parts to what I posted earlier in a little bit.

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