This is dead simple in Vegas 4 (I assume you have Vegas if you have DVD Architect.) You can simply render to PAL specs instead of NTSC specs with the MainConcept MPEG2 render controls. Then go back to DVDA and create a new project with PAL default settings. Import your PAL media and you are all set.
I've done a couple of PAL versions of NTSC projects. The results sure beat what I used to get with a multi-format VHS VCR!