Photoshop and Illustrator are both amazing. Logo's tend to need various sizes (web, letterhead, business card, posters, vehicle vinyls, etc ...) so vector art is usually preferable to bitmap art as it scales without creating visual artifacts. This alone points towards illustrator being the more attractive of the two although I must admit I am much happier creating a large bitmap image (say 5000px) and then scaling downwards.
But if you're creating logo's professionally then you really need to get into vector art as it is more or less expected these days.
On the bitmap side of things, GIMP isn't as easy to use as Photoshop, nor is it as capable* but it is free (as in beer) and certainly has plenty of creative flex in it. It is the de-facto graphic design software in the open-source arena bar none.
If you don't feel too uncomfortable with vector design then I'd definitely suggest Illustrator, but if not I'd say try to borrow a photoshop installer from someone who has moved to a newer version or obtain a trial if possible, even if it is an earlier version from a coverCD or such. PS has been so good for so long that even the pre-CS# stuff (more than four major versions ago) is still wickedly capable.
*Just my opinion, other peoples experiences will vary.