I have no idea about anything with .SAT files and mp3 conversion or how that happened...but...despite the extra time I say congrats.
My gigabeat is the S model, the one that somewhat became the Zune a short time later...so it didn't really use the Toshiba stuff but was a Windows Media powered device...even though I've got a disc that came with it...when I first plugged it in...all kinds of stuff gladly asked if i wanted it to manage the media collection...and being an MTP device, that's about what I expected. Even my ubuntu install popped up with MTP client software. I never actually tried any of the software...all I ever did with the original firmware was boot it up and look at it and go "eww". But unlike the older gigabeats which used toshiba's stuff..the s specifically is an MTP device...which I'm sure probably changes things.
despite that, the gigabeats have been touted as some of the best devices to run Rockbox on. since you stated you have a 40 gig...it'd almost have to be an F as the 40 gig was dropped with the X models. But it's got a 300mhz ARM core...32MB ram..wolfson WM8751L dac...it's a pretty beefy unit for running Rockbox...most ports in the past were generally with less powerful hardware (i think...too much research). My S has a beffier ARM cpu and more ram...but even then Rockbox apparently only runs the CPU at around 250Mhz (it's capable of 533). I had an iPod 5.5 30gig in the past...and it was a portalplayer based unit that had a dual-core arm cpu...but they only clocked them at around 75mhz (although for a while I had it overclocked to 90) and it struggled to do some things.
as far as SAT files go...according to the research i stumbled upon when looking up gigabeat specs...it's an encrypted wrapper for the mp3...why vista did this conversion for you...i have no idea...i'm kind of blinking in surprise on that one.
She can change sources, channels, etc etc without even looking down. I would like to retain that type of interface for her.
yeah, rockbox isn't for you then. Mind you, back when I had my ipod...they had no information on the serial interface. This was about 2 years ago. I just checked the status and they've written a serial port driver and some accessory protocol have been documented....but I don't know how much and to what degree it works...it's not fully functional. as stated, you'd have to find an older ipod on ebay in order to run rockbox on it.
http://www.rockbox.org/wiki/IpodPort is the best source for information on what rockbox can do on what ipod. At the bottom under other pages of interest, there's a link to the ipodstatus which will give more indepth information. Actually, if you search the wiki you can find very similar pages for all targets and even information on the status of attepted ports.
It's not a piece of software for everyone..it has some very odd ways of working that take some getting used to, especially if you're used to using an iPod already. It took me a couple of days to learn it with no prior knowledge of how newer media players interfaces worked (i'd used an ipod for maybe a total of 20 minutes)...and of all the friends of mine that tried to play with it...the one that hadn't ever owned or used an ipod figured it out where the ipod users got confused and angry. It does however completely break the ipod hardware free of the apple imposed restrictions and turns it in to a very nice flexable piece of hardware, much like it does to any unit you stick it on.