Vista is still being avoided like the plague by many corporate IT departments. If it wasn't for computers sold in the big box stores including it, it would've gone the way of Windows ME and I hope it goes soon. Everyone I personally know who has Vista has problems with it. I know people posting here have fewer problems or have licked them, but it's tough for many users. XP64 is not a bad option if your new PC is just meant for specific applications like Vue that run fine on XP64. Read up first to make an informed decision. It could also save you some money.

The original poster should dig more into his settings to see if something is amiss. Also, if it's a dual core rig, the 4GB would be split in half between cores and a good part of RAM (at least 500MB) is always reserved for system functions. That could be a reason why it only goes up to 1.5GB of usage. I think some Vue processes are single core only. I could be wrong.