Try the following:
1) Copy contents from App1 & App2 DVD's to separate folders on the hard drive.
2) Name them Adobe CS4 App1 & Adobe CS4 App2
3) Run the App1 setup.exe program from the Hard drive and in a few minutes the serial number page should appear
4) Setup goes through the process as you would expect.
OR IF THIS DIDN'T WORK:
1) When the setup hangs at about 90%, open task manager but do not close setup.exe yet. (ctrl+alt+delete)
2) Go to start>run and type in appwiz.cpl (or open programs and features from control panel - add/remove programs in xp control panel)
3) You should see whatever you attempted to install show up in the program list. Click on it as if you were going to uninstall it.
4) Once it is highlighted (without running uninstall) close setup.exe using the task manager in step one then click uninstall in the program list. setup should continue as usual.
OR IF THIS DIDN'T WORK
Try running the Adobe CS4 Cleanup Script:
I Hope This Helps...