VGA to DVI?

I have a nearly new XP machine. I also have a new Win7 machine. I continually work on other computers for our computer club.

I have bought a 4 port KVM switch with DVI in and out. My XP machine (although it has a DVI connection on the back of the video card) won't connect. I have now added a DVI to VGA connector at the XP machine. Still won't recognize the monitor. The Win7 machine has no problem with it.

Thoughts? Thanks

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