I'm just not much of a computer expert to give you any advice. I have installed it on several machines, laptops and PC's, and never had any problems at all.
Only other things I can think of are making sure you have a recent update to DirectX, and if all else fails, trying to reinstall. I also think there is a link on the camelotherald.com to get a set of installation disks sent to you.
However, if you are planning on playing the game past the trial date, then I would suggest you buy the 5th anniversary edition. You can buy it online and have it in a day or two, and although it may cost $15 or something, you get the first month free, so it is essentially free. Doing this will give you all the expansions, including Darkness Fire and Labyrinth of the Minotaur. If you were to purchase them in-game, they would cost $30 and not give you a free month. If you need a link for any of this, let me know and I will be happy to find one for you.
Edited, Jul 28th 2008 2:17pm by thuri