Step 1: Recon
First and foremost, get full and accurate specs on all of the hardware. RAM, hard drive, CPU, etc. This will determine if going to Win 7 is practical. If they've got a bunch of Pentiums or, worse, Celerons, with under 512 MB RAM (entirely possible for a basic XP install) then odds are that they're going to need new hardware before you do anything else.
If the hardware is adequate then get a list of all, repeat, ALL, software currently installed and any additional software which might be required. From that list you can determine if it's even possible to go the Linux route. Remember that if they have Windows-based software then retraining with Linux-based systems may (that is, WILL) be necessary and that will take time and budget, too. Also, if they depend on anyone else for support, and whoever that is doesn't know Linux-based systems they will have to get new support. This may be difficult out in the middle of nowhere. Check with the actual users and determine exactly what use the various apps are put to; if they need, say, to support MS Office macros, then Libre Office will NOT work. Sorry, it won't. If they need to exchange documents with someone who uses MS Office, then, depending on how complex the documents are, Libre Office _might_ work... or might not. It is fairly easy to generate documents in Word, Excel, and PowerPoint which have severe problems when round-tripping to Libre Office. (It's easy to generate MS Office 2010 documents which have severe problems round-tripping to Office 2003, much less, so you'd better check to see what the people they have to talk to are using...)
Step 2 Logistics
Having determined the extent of the problem, build a disk image with your fav imaging software around the hardware and software required. Depending on the size of the image, haul it in on DVD, a thumb drive, an external USB drive, a computer of some kind with networking support (switch/router/whatever). I'd go with a computer. Set up a network if not already in place (leave the network when you go) and run the image over the network to the systems. With only eight systems to update this shouldn't take long. Leave the computer as the admin system for the network. Note that the computer need not be a Windows system, depending on what imaging software you use. The image should have the latest versions of all software, including AV, and updaters if necessary, so as to not strain the Internet link.
Step 3: Consolidation
The support computer should have the ability to back up the network and should be connected to the (yes, I know) satellite connection so that someone can remotely admin it. If you go with a Linux system instead of Win 7 then this will help with the support problem, but may not be enough, depending on exactly what apps they need and how they need to use them. The support computer should be configured as an update server; all updates come in _once_, to spare the satellite link, and then get sent out over the network. This also could make security better.
A Linux-based system is unlikely to suffice. (Sorry, Tuxers, but we're in a Windows world.) And, besides, the mission brief is to move to Win 7. Unless you can convince the users that Linux would be better for them... and support them thereafter.