You will run into problems, as core libraries have changed in 12.04, rendering many TDE 3.5.13 modules unable to compile on that platform.
Is this desire to compile from source related to the nightly build mirror problems?
Well, of course. For weeks now I am on XFCE using what's left from the last installation. I like XFCE, but it doesn't play too nice with kde apps in terms of session management and other things, and I'd much prefer to have Trinity back.