sjcollier,
I just did what you're planning to do 4 months ago. You'll need (what OSCAR said) the vga breakout cable. You could hack one yourself, but I just picked one up when I ordered the arcadeVGA card.
Also, I ordered the 19" monitor from Happ. It came with wires for R, G, B, sync, and ground coming out of a molex connector on the monitor chasis and a power cable. That monitor had a weird squealing noise and ended up dying. They sent me a new one that works great but there was no power cable.
You can order the power cable separately from Happ. I think they may have made a mistake on my first order and sent me a free power cable.
As far as the isolation transformer goes, the Happ monitors don't need one. You can always ask a sales rep, they're good with returning emails.