No it’s not open source but it is available for both Linux and Windows.
IncentivesPro make a product I recently used for a Virtual Desktop Thin Client Implementation. That is USB Redirection for Remote Desktop. It uses a proprietary client/server and so I used Windows XP embedded thin clients to redirect specialised USB Thermal Laser Printers to the Vista Virtual Machines. The website looks a bit underwhelming but the product is flawless and it’s priced much better than their competitors. If you have more time than I did, it’s likely you can get the Linux client working with Thinstation
For the other desktops, I used 2x’s Thin Client Server that use PXE (or USB / CDRom) to boot the original desktops over the network, essentially converting the original desktops into diskless thin clients. It’s a shame you can’t build your own images or add your own software to 2x’s desktop as I really didn’t like having to implement the Windows XP embedded thin clients.
As it’s a small environment, we are using VMWare Vsphere 4.0 free version. I was aiming to use Xenserver 5.5 but it doesn’t natively support Tape Drive passthrough to the client and I wanted to easily accomplish this without kernel rebuilds, as it is possible to achieve this with Xen by recompiling the kernel with ISCSI support and making the Tape Drive an ISCSI target.
Some other useful software was SplitView, allowing the accountant to use Dual Monitors. RDP 5.2 only allows to use the mstsc.exe /span option which spans the monitor across two screens. Splitview allows you to manage those windows as individual desktops. The only issue I had was with Adobe Reader 9.2, I had to add it to the exceptions list in Splitview otherwise it would crash.