Sims 2 University Ex Pk Installation Problem

anyone have a problem installing this?
its for my 9 year old niece and would love to sort it out for her.

while installing the whole installation will hang at 78% (which is right at the time you swap disc 1 for disc 2

the current file loading at the time is
"TSData\Control\control1.dat"

she already has Sims 2 so its not that.
the PC has half a gig of RAM and is running XP with a Pentium 4 processor, with about 10GB hard disk space.
i've removed loads of unused programs, defragmented the hard drive, uninstalled Sims2 and re-installled it also.
if she is already able to run Sims 2 she should be able to run the expansion packs also??

any help would be greatly appricated.

 

You might want to check the disk and see if it needs cleaning or has any scratches on it.