Game not supporting resolution once had

When I started playing the game again, I was playing it on my widescreen TV (42' LCD) with the resolution of 1360x768. The game gave me all the options my current video card is capable of supporting (Radeon X1600 Pro) and all was fine.
Couple weeks later I went back to using my 17' LCD non-widescreen monitor thus having to change my resolution to support 4:3 ratio - 1280x1024 - so it does not look distorted.
Now, for my own reasons, I want to go back to playing on my 42' widescreen. So I change the resolution back to 1360x768 on my PC, plug the VGA cable in to the back of my TV and launch the game. I then go in to my graphics option to turn the game resolution from 1280x1024 to 1360x768 but I can't. The resolutions I once had to chose from are now gone. I can change the resolution(s) fine on my desktop but I cannot in game anymore. Anyone know how to fix this?
I have tried downloading and installing the latest video card drivers and it had no effect on my options. I would rather not have to reinstall the game itself (downloading all those files at every single zone - I would like to try and avoid).

Can't see the imageshack shots, so just guesswork from me. Have you "told" your graphics card what monitor you're using? It may still be assuming that you're still using your 17", in which case it will only offer the resolutions compatible with that.

[edit] - except you already said windows runs happily at that resolution >< I think it may be related, though.

[edit2] By the way, if you ever do need to "re-instal" the game, there's never a need to download files in every zone. You just use the -image switch in the GW shortcut. (Ask again if you haven't heard of that).

[edit3]hnnnngggg - sorry. It may well be that windows will happily run widescreen res on a 4:3 monitor, but GW won't. Check your graphics preferences and ensure it says Radeon x1600 via (whatever 42" monitor). If it says it's running on (your 17" monitor) then that's your problem. If it says (as is usual) ...on a plug-and-play monitor, then it's got it wrong.

[edit4]Please, someone step in if I'm talking total bollocks - I'm running out of edits and into waffles

Thank you, Snograt, for your suggestions. My display was reading as a "Default Plug and Play Monitor". I went into my Catalyst Control Centre that came with my video card drivers and forced it to read the now "Default VGA Monitor", did a quick reboot, and now I can use the desired resolutions that work well with my TV.
I missed playing Guild Wars on my TV. Thanks!

By the way, what is the -image switch in the shortcut you are talking about? Sounds useful if I ever need to do a re-install.

All you'll ever need to know about command lines:
http://wiki.guildwars.com/wiki/Command_line

Well maybe not all but the necessary info is there

Yup, that's a good link. What the -image switch does is download ALL the data in one lengthy session - all the maps, skill updates, everything. If you have a slow connection it can be an overnight job, but it's well worth it.