The most obvious answer is to insist that your IT guys install some DVD playback software on your computer.- it shouldn't be difficult. PowerDVD and WinDVD are the most popular and can be bought for less than the price of any lead.
Failing that if your PC is too old, your projector should have a yellow "phono" type connector which accepts a composite video input. You would need a lead that was a scart socket at one end to a "composite video + Left/Right Audio" on the other end. The quality from this connection would make a home cinema enthusiast cringe, but for classroom use we find it more than adequate (I am an IT engineer who works in primary schools.) the red and white connections go to the sound system and the yellow connection goes to the projector.
http://www.maplin.co.uk/module.aspx?...28102&doy=26m9
If the projector is too high up you can always extend the yellow wire with this:
http://www.maplin.co.uk/module.aspx?...=9664&doy=26m9
Converting a scart or composite signal to VGA is not really a good option as any device which does this is likely to be both expensive and not very effective
Hope this helps you
Dave