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Every time I try to install programs in Windows 7 (the guest) that I already use in Windows XP (the host) I get the message: This is not a valid Win 32 Application. I am running Windows 7 in a virtual folder environment alongside XP. When I mount my CD ROM in Windows 7 it recognises the CD and lists its content, (although in some instances it does not list all the programs on the CD data disc). When I click on any .exe file to install a program I get the above message. In effect it means I can't evaluate Windows 7,as I can't install my motherboard or video card drivers or set up my broad band internet. Any help would be much appreciated. My version of VisualBox is 3.0.0 49315 Thank you.

Have you tried 3.0.2 yet?

First you can't install the video, motherboard, or broadband drivers in a Win7 RC guest because it is running virtualized and those drivers are not what VirtualBox uses. The other problem is due to a signing issue and Windows 7RC having a problem installing unsigned programs/drivers. You can however get past this by turning it off.
Google this driver signing issues in windows 7.
Needless to say this is a Windows problem and not a VirtualBox problem.

Thank you very much for your help. Am I right in saying that if I convert the Windows ISO file to a normanl Windows installation file and ran it in a separate partition i.e. dual boot I could install all programs including motherboard drivers?

The installation is not the problem, where you install it is. Inside VBox the hardware is emulated and support only one set of drivers (the GA). Some exceptions are the lan and sound drivers but not any motherboard drivers.