You really need to think about what you’re doing and why to send yourself in the right direction.
Given the cameras you mention you need to decide tape vs tapeless and HDV vs XDCAM EX as well as interchangeable lens or not.
You need to think not only about your NLE software but can the CPU you have handle MPEG2 Long GOP and/or have the resources to convert it.
My own biases. I do NOT like the HDV codec at all. Tapeless can be better than tape in most situations. With EX3 announced you’ll have choice between fixed (EX1) or interchangeable (EX3) lens camera.
I’m a Mac person but I certainly can understand delaying the cost of Mac plus Final Cut Studio until next year if you’re going to spend your budget on a good camera and accessories this year.
Adobe is coming out (has come out) with an update for Premiere Pro CS3 to handle the XDCAM EX files directly.
Now we come to your current system. If you can get Premiere Pro to run on your system AND your system specs can handle MPEG2 Long GOP you’d be on your way.
That last part is toughest since you haven’t said why you can’t get PP CS3 to run nor anything about your CPU specs.
The EX downconverts to SD out of SDI or you can do it in software. The first requires SDI input to your system and the 2nd requires rendering. If you don’t already have SDI in and your CPU means a slow render then you really have to consider updating your system even to handle SD . . . in which case you’d also be able to handle HD.
Since you have CS3 and seem not to have the budget to go Mac yet, you might just get a capable Windows box. BTW you might ask Adobe if they have a crossgrade program since they do have Premier Pro CS3 for Mac. This way you can get a Mac instead and use PP CS3 which you already have.