Loading Ubuntu 7.04

My apologies if this has been covered, but this is my first try at Ubuntu.
I have been given an old Pentium 3 Dell pc, it has a dodgy copy of XP pro on that I obviously don't want to use. It seemed a good idea to try to increase my knowledge and try a Unix based os - Ubuntu was recommended to me.
I have downloaded 7.04 and burnt a boot disc from the ISO. i have changed the Bios to boot from CD. When I start the machine it boots up to Ubuntu and then I get the desktop screen ok. I have even been able to adjust the mouse pointer speed.But after that the machine just seems to 'hang'. I have left it for about half an hour and all that happens is the screen goes blank but the CD reader seems to be still trying to load something. Am I just being impatient? Should I give it more time, or do I have a problem? I've not seen any error messages that I can report.
Any help gratefully received.
tim