Thanks for this quick tutorial jakiman. Buffer size did not work on my main card, so I had to lower it to 2432 though. Some utc love coming your way!
Actually I had a hunch that if it is my main card, it is probably out of memory, due to some visual stuff. I tuned down all the visual things in windows 7 and 2560 is now a go!
Woohoo. I'm glad you got it sorted and also glad I was of some help.

Thank you for the UTC! You were the first and only one to tip me for it...
It was nice to see you understood how it all goes together and that someone's finally gotten a tip by explaining it
For anyone who wants the full knitty-gritty that Jakiman's summarized, the full documentation and explanation can be found here
starting around line 56.