Hey, I know this is an old game, but Tesco had it for £10 so I thought I'd get it even though I've already completed it on the PC (for achievements and just generally to relive the experience).
Anyway, there's this one level - Testchamber 18. The last part of this is really the only 'action' part of the game because you have to reposition the portals while flying through the air. It's pretty tricky on the PC with the mouse, but I got it done eventually. I spent ages (well, an hour or so which is a long time for me and a game!) trying to do it with the joypad, but it seems impossible. Has anyone got any tips they want to share or is this something only people who play Halo/COD 16 hours a day can hope to achieve?