Hi and welcome to the forum.
When you say freeze what exactly does that mean and what to you do to "unfreeze"? you just cancel the conversion? or you have to abort the program from task manager? Is ConvertXtoDVD creating log files of these conversions? If you can you paste a log file here? (you will find the log file here C:\Documents and Settings[your name]\Application Data\Vso)
You mention this other programme running? can you stop it and see what happens if you convert without ANYTHING else running?
Could your system be overheating? is there a screen saver that goes into actions?