I know all about passme and flashme but I am wondering how the roms actually work.

I have a 256m xg flash GBA card and I want to use it to run DS roms so I dont have to carry all my games around and switching them in and out.

So do any current NDS backup products have multi-rom support?
Do any NDS backup products have the ability to save multiple game's gamesaves directly to the GBA card or to a SINGLE DS game?

I dont mind having a retail DS game in the slot in order to save games but I dont want to have to have a different DS game each time I want to save.

So, in summary, is there a backup solution with these features or should I wait a bit longer. I have a version 1 DS by the way.

Well, I can't speak for regular GBA flash cards but I'm using a Supercard SD for my games. Works a treat.
I used the wifime trick to load flashme so I don't need a passme device.