I didn't have any problems what so ever installing the 2008 trial, I used the 32bit on vista ult. 32bit, are you using the 64bit or something?
mayby you should extract the files from the zipper and burn them on a disk with the autorun file?
I've seen it before where they ask "insert disk" eventhough the disk is inserted, so when you copy the files to the HD and start it from there, it installs without problems?.. (reverse psychology in software) or redownload the trial mayby something went wrong?
Intel 7 - 2.8Ghz
NVidia Quadro 4000 2Gb GDDR5
8Gb RAM
3D Studio Max Design 2013 x64
Windows 7 x64
http://www.3dboomerang.com/