The major differences between SD-80 and SD-90 are form factor (80 is a 1U half-rack module while 90 is geared for sticking on top of a desk), screen size (80 is just 2-lines; 90's is a bit larger) and audio input ports (80 lacks these). Otherwise they are identical. Instruments are based on those in the professional Roland JV/XV lines of synthesisers.
Reed Romance is included in both, as Patch #41 in Special Set 2.
They will run on Win7 as both MIDI and audio devices with the latest drivers.
You can use them with any sequencer or DAW of your choice in combination with the SD-80 Editor (NOT the GM2 one), which allows for precise tweaking of the instrument parameters. You can alternatively use any patch librarian software or even edit directly with the hardware panels to do the same, especially on Lion-based Macs (the editor app is PowerPC and therefore no longer works).
Roland offers the drivers, software, and manual for these synths for free, so take advantage of them! That manual will be especially handy for knowing its capabilities, even though it's a very dense read.
Now, as for buying with a good price, all I can say is keep hunting on eBay for now. Only one now is a US$535 one, though. And don't go for SD-20s either, as they have considerably reduced features (owner of that as well).
