My box:

Athlon 2200+ or something, 768MB DDR 2100, Sapphire Radeon 9600XT 128MB.
Samtron 76E 17", Logitech MX310, Everglide Razer Attack Pad.
Maxtor 60GB, Seagate 60GB, Maxtor 160GB and a NEC1300A +-DVDRW.

"New" Games, can't access filename.cab error

You're sitting there, trying to install a game, but right when it's about to start copying files to your precious harddrive, it gives you an error about not being able to access filename.cab, seen it before? Well, this is how I solved it:

Make a backup of your registry before doing this, I take no responsibility for what you do to your computer.

I opened regedit (regedit in run), browsed my way to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
and located the REG_SZ: allocatecdroms. Which in my case was set to a "1". Change that "1" to a "0" by double-clicking allocatecdroms, and change it. I then proceeded with a reboot, it is perhaps possible with a reboot, but it felt nice. After that, the copying of the files worked just fine. This fixed these errors I got when trying to install the games Manhunt and Far Cry, on my box.
So if this doesn't work, please try out this site: Microsoft Support Games: Error Message: Setup Failed to Extract Files from .CAB and this one from IGN Boards Help. Can't install Far Cry.