ok here is a list of the parts you will need and the tools to fit them:
headset. it is likely to be a 1 1/8 inch size as it isn't a road frame
front fork (rigid or suspension) make sure steerer will fit the headset (1 1/8)
bottom bracket. there are different sizes for these so you may need either a local bikeshop or trial and error for this. basically its either 68 or 73 mm for the shell, and the other measurement is for the lenth of the bit the cranks fit on. common measurements are 68/113 or 73/113.you will need a bottom bracket tool and an adjustable spanner to fit this. remember, one side screws in in the opposite direction to normal (reverse threaded) so don't force it the wrong way.
crankset or chainset (same thing really). these are the driving cranks. most decent cranks these days need allan (hex) keys to fit so a good investment is a set of allan keys with a large range of sizes from 3 to 10 sizing.
pedals. adjustable spanner needed to put on to the cranks.
front and rear derailleur. these are also called mechs. they are the bits that change the gear. the front is pretty much compatable with any number of chain rings on the cranks but make sure it is compatable. it should say if it isn't. the rear can be a range of gear numbers, so if you want 9 gears on the back, make sure the mech is compatable.
shifters. these are the gear levers so make sure they match the number of gear rings u have.
cassette. this is the rear gear ring assembly. you will nead a cassette tool and an adjustable spanner for it. (and something called a chain whip if you ever need to take it off)
chain. make sure a 9 speed chain goes on a 9 speed setup etc.
gear cables. the shifters usually come with these, but make sure.
brakes. discs or v? v brakes are cheaper. discs are only really worth it if you go hydraulic but that costs a lot. front and rear. make sure the brake levers are for cable or hydraulic.
stem. holds the handlebars onto the fork.
handlebars
grips.
seat post and collar. make sure these are the right size for your frame. (online or ruler)
saddle.
spacers can be used to raise the hight of the handlebars.
wheels. front and rear. (make sure rear is compatable with the cassette size and make.
altho that seems a lot to take in, basically it comes down to, lots of allan key work, the occasional spanner job. greasing every single bolt. making sure everything is tight. a bit of trial and error (especially with the mechs). and really, spending more gets you better as a general rule.
www.chainreactioncycles.com is good as they often have sales and you can get good stuff cheaper. ebay is also good.
shimano deore, deore lx and deore xt are good average priced componants. but hunt around the web and see what you can get