Hi there... You should have few problems with this setup, but you'll need to get Intel chipset and RAID drivers either from Dell or Intel.com after the installation. You may notice freezing right after installing and this is because you do not have these drivers installed. How do I know this? I have tested it on an XPS 410.
For upgrades run the Vista Compatibility Advisor which you can get at Windows Vista Home Page. When you run the install it will also run a check before you go to install the OS. The only problem I see here is whereas in the beta it prevented you from installing if you would have errors it lets you now and just gives you a warning to remove the programs. This is especially the case with ZoneAlarm firewall. Remove anti-virus and any third party anti-spyware/firewall programs before you install or you will get errors on start-up.
Prepare to do a fresh install in case the upgrade fails or has errors since it can and will happen to some people due to software incompatibilities on their machine. Depending on the size of your existing hard drive you could get an external and just back up most of your important files on there. I would do a clean install and not even risk the problems you could have but thats just me.