I'll have to second the Compaq problems. I've *heard* that HP is OK but dear lord .... don't get Compaq no matter what. Oh the misery.
As someone who is probably one of the rarer people who will give you a balanced view of OSX vs. Windows XP, I have to say it really depends. When I bought my iBook a few years ago I thought that it totally was not worth the price, and there are some software compatibility issues. Currently, however, I really do think that the newest products on the Apple line are pretty nice, particularly the MacBook Pro, but it doesn't look like you want to spend $2000 on a new laptop, even if it can run both Windows and OSX.
Also, I don't know how computer-savvy your parents are; OSX does take a little getting used to for some people, and they find the more intuitive arrangement of the file system confusing. Basically, a lot of the Mac stuff is designed well, but for the money (if you are looking for more low-end stuff) I think you should go with the Dell since you get more processing power / $.
(I mean, ideally you would want one of the new super-powered AMD dual-core processors that blow Intel out of the water, but, you know--can't have everything

)
For photo editing options, I think the key is to buy good software; a must-have would be something like Adobe Photoshop. :thumbup: