mountain bike advice

I'd put you on a 19" bike. You're a couple inches taller than me and I can ride between a 17.5 to a 19, depending on the brand.

I'd recommend a Gary Fisher Marlin Disc. It's a good starting point for a hardtail for the money and GF has a lifetime warrenty on their frames. Also, the Trek 6000 is a good bike too. Check out trekbikes.com and fisherbikes.com. Trek also has a lifetime frame warrenty.

In that price range you're gonna get decent components on a HT. You'll probably see at least the Deore group or Sram X-5. I'd also look for Avid mechanical disc brakes, either the BB5's or BB7's. Hydraulic brakes are nice once they're set up correctly but mechanical disc brakes are easier to work on at home and they're less expensive.