You CAN use them on Sony/Minolta AF cameras's, you just need an adaptor.
SRB Griturn sell one for £42.
You can also get adaptors to Canon and Nikon from Roxsen. They are about £20, come from the states and you'd have to buy through eBay. Minolta MD to Nikon is
here and Minolta MD to Canon EOS is
here
Whether it's worth spending the money on the adaptor really depends on what lenses they are though. Also remember that because the adaptors add extra length (albeit a small amount) you can find that your focus is off. It's common with Canon to Nikon (and vice versa) convertors that infinity focus is actually slightly off once you use the adaptor. The Roxsen Minolta to Canon convertor says it's got true infinity and I don't know if it's a problem with Nikon.