Tron,
I'm assuming you are streaming from your Slingbox to your laptop? The Dell XPS should be butch enough to handle everything you want to do with it. The only exception being your CAD programs which may require more 3D acceleration then most low to mid range laptops can offer. That said, the bottle neck you will hit will be memory. Get a model that can support up to 4 Gb's of DDR2 ram. Load it up with 2 Gb's initially.
If you're worried about the video performance, you can upgrade that Dell to use the Geforce Go 8400. It comes with it's own dedicated memory, which is a big help! The upgrade is only $80 so it's probably worth it. If you buy your own memory upgrades, you can recover that cost easily.
120Gb-160Gb of disk space is pretty standard these days so you shouldn't have any issue with storage.
Overall, yes you will be able to get a machine to cover your needs for ~1500$. I personally don't like the Dell's because they feel flimsy. Same with Acer's. The recent HP's come with fairly sturdy cases though. This is important to me mostly because I'm paranoid about damaging the LCD screen.
Hope that helps.