In reply to VwJap:
Maybe asking more specific questions would get you more answers.
But here's a couple of points,
The fitter you are, the more you will enjoy the base camp trek. Get a good level of fitness (be it running/cycling, anything really) before you go.
Saying that, the best thing you can do over the summer is get outside and walk lots in the hills. If you cant do that, walk everywhere, down the shops, to work etc.
Invest in a good pair of boots, decent waterproofs and a good sleeping bag (you'll need one for the trek)
You can read about my base camp (and some extras) trek here
http://tankgetshigh.wordpress.com/ (you'll have to scroll through to get to the older posts, and avoid the salesy bits :P)