Argh! So, Im going to dual boot, off a External. If possible Windows on my primaryHDD and a linux system (Ubuntu) on a 250g IDE... teeny issue with that though, I will be using ubuntu for just music & video and working on internet. any other OS thats better for that? I heard ubuntu/Linux is awesome and isnt heavy on the cpu.
That's odd, since to my knowledge Windows is still the most user-friendly OS for multimedia playback and gaming. Also, with regards to CPU usage, I doubt there will be too much difference between Ubuntu and Windows 7; W7 has been optimised for power consumption and shouldn't be as taxing on a computer system as Vista was. And Ubuntu not being CPU-heavy is a myth; it all depends on how you use it. If you decide to go and enable most of the Compiz effects and basically use Ubuntu the way many people use Windows, it is just as CPU-heavy. That said, if you finally decide to try out Linux, more power to you.
On a final note, I am going to strongly discourage you against booting off an external drive. If it's a thin system like Puppy Linux or DSL (Damn Small Linux), perhaps it's not such a major issue. A fully featured Linux distro like Ubuntu is going to have many more files than a thin system, all of which will be accessed in quite a random manner. This means that the higher latency of an external drive is going to severely impact your experience, especially when accessed over USB.
I'd suggest getting a speedy 8-16GB flash drive (i.e. thumbdrive) for the OS and your applications, and perhaps another external (the 250GB IDE drive) for larger files and documents. The lower latency of Flash should help things out quite a bit (still won't be as speedy as a native internal install though), and you won't be crippled by the small storage space of a thumb drive.
You're free to go ahead and boot off the IDE, of course, just wanted to make sure you're aware that it may be much slower than you wished.