Bloomberg.com tells me $900CAN = $592US. So that's plenty of money to build a good system without monitor. The XP2000+ is listed on Pricewatch for $130 (all figures in USD btw). That's probably your best bet.
If you're not overclocking, PC2100 will probably do, as the Athlon bus runs at that speed. Going from PC2100 to PC2700 at 133fsb does not get you much from what I've seen. I do recommend getting 512MB though. Grab a stick of Samsung PC2100 for $100-110.
Case and power supply: not sure what to tell you here, but the Antec SX635 might be a good bet. It comes with a 350W PS, which should be more than enough, and sells shipped for <$100. You might be able to save a few bills by looking at other brands and models though.
Motherboard: many, many opinions on brand and model, so I'll start with chipset. The KT266a should meet your needs. It's solid and mature, and I don't think you'll benefit by going to the KT333. The n-Force boards are always an option tho... anyway, someone will have a good recommendation here but until then consider the Asus A7V266-E with onboard audio. $100 shipped. There are probably boards that meet your needs for significantly less though.
Hard drive: I have a Deskstar 120GXP that's big, fast as heck, and sells for <$100 for the 80GB model. Of course Deskstars have a bad reputation for reliability now, but I haven't heard anything regarding the 120GXP model so I took a risk. Anyway, if you are more risk-averse go for the WD 800BB, 80GB and sells for about $100 shipped.
Wow, we are almost out of money but that's fine -- the last item (I won't even bother with floppy) is cheap: CD-RW. Try a Lite-On 32X12X40. You can get one for <$60 shipped.
That's a good starting point. Hopefully others will give you better info on the individual components. Stick with the XP2000+, though, and don't go for less than 512MB unless you feel like adding another stick in 6 months.
jaybee
Edit: Oops! I forgot all about the video. Crap... well, you can save a little money by going for an n-Force board and getting the built-in audio. Maybe an Asus A7N board. The 60GB WD600BB would save you about $25 over what I mention above. Anyway, bust your budget by about $40US and get a GF3 Ti200, or spend another $10 for the Radeon 8500. You did say about $900CAN 😉
Edit: Also, don't worry too much about the heatsink/fan. The retail hsf will be good enough at stock speeds. The retail cpu goes for $155 at googlegear btw.
