I’ve done it! I’m now 100% Ubuntu (all on 7.04).
In the process of setting up my file server, I discovered that installing the nfs-common package on my other machines really helped their sluggish NFS behavior. A good reference for things to do after installing Ubuntu 7.04 is 13 Must Do things on new Ubuntu 7.04 Feisty Fawn installation.
I installed envy (nVidia driver installer) but, for some reason, the new video card isn’t properly detected . I may try manually installing the driver later.