I'm surprised that you are able to use a 30GB backup mdb back-end at all... the MS Access limitation is 2GB, for both Jet 4 and for MSDE. Check out this article here-
http://sqlserver2000.databases.aspfaq.com/what-are-the-capacities-of-access-sql-server-and-msde.html . I believe in taking things to the limit, but this is way too extreme.
Bert asks very pertinent questions about the cards, switch/hub, cables, etc. you might wish to try the newer 1000 mbps cards, switches, and cables. BTW, what type of CPUs do the Lenovo clients have?
If you get rid of the pictures, then compact your back-end your system should fly. With a Jet 4 back-end you shouldn't have any pictures- none, nichts, никой, कोई नहीं, καμία, nada, لا شيء, rien, nic, ingen ting, 何もない, niente.*
I've seen well over 15000 patients over 20 years with a partner, and without pics my back-end still is under 100MB. As you can see from the article above, it's not the number of patients, diagnoses, etc... it's the overall size of a database which is the problem.
Are the pictures that important to you? If so, you might wish to place them into a container of choice, s.a. OneNote, Evernote, GoBinder, Powerpoint, PDFs, or Word and make virtual "charts" of graphic files. You can use Windows Explorer or any other of the many document management systems (do a search on emrupdate for the numerous threads on DMS programs).
*versions of "none" thanks to Google Translate.
