While installling VS 2008, you may encounter cannot open deffactory error. To solve this, just copy/paste following highlighted text in deffactory.dat file and setup will continue :)
[Version]
Signature = "$Windows NT$"
Provider="Microsoft Visual Studio 2005 Professional Edition - ENU"
Version=800.100.00
NullString=Null String
Lang=1033
[Scenario List]
vsscenario.dll
[Scenario Factory Information]
Default Scenario=11E4C8F3-425E-43b9-B689-8BFDF03342E2
a429d00d-060d-42b1-a782-61928a65cde3|1|3.0
visual studio