It is very easy, I've managed it, so it must be.
Also it'll improve you confidence on general bike maintenance, as you realise it not black magic..
The hard part is making sure you have everything you need and it's all compatible. Get this right before you start and your on to a winner. So investigate the stuff like gear compatibility (seemingly more niggly nowadays with 10 speed stuff) seatpost sizing, front mech size, fork steerer length, what brake adapters (& maybe shims) your going to need throughly, buy the right kit and bolt it all together, dead easy
Tools, a decent and I mean really good set of allen (hex) keys are a great start (£20 Halford Professional set for me). A set of cable cutters, doesn't have to be bike specific (screwfix £6) is useful.
Edit: As I've missed the obvious cassette tool & chainwhip... though mine came in a cheap kit but have last ages & work fine.
Headsets can be fitted using a mallet (if your brave) or DIY tools like this, though the BB will require a special tool of some sort (HT II normally) & I'd suggest buying one of those.
This site dead useful for guides on how to do stuff:
http://www.parktool.com/blog/repair-help