iMac hung on blue screen/error found


... somewhere in B.C. ...
Please, I need some help with the following:
I've moved my iMac. When I went to start it up after moving it it wouldn't start. It would hang on a blue screen and just sit there.
I tried using all the little tricks in the book that came with it to try and get it going, all to no avail.
So, today at lunch I phoned the Mac helpline. Thankfully I bought the computer on November 10, so it is still in the three month window of free phone help.
The guy basically gets me to run a utility on one of the installation DVD's. It said that it found an error and fixed it, however when I tried restarting it the problem was still there.
So, I had to do a complete new reinstall while it supposedly saved the files.
All this took like two hours, so I was late coming back to work.
When I left home it looked like the old OS was on, but I still need to do the upgrade to Leopard. All the files seem to be there under a separate file in the finder, but when I tried to transfer them over it said I had no space.
.... now what?
(iMac 20", 2.0 GHz, Intel Core 2 Duo, 250 GB, came with Tiger, upgraded to Leopard)