Virutally every image viewer (and even the windows explorer interface) allows you to access basic EXIF info like camera make/model + exposure settings. There shouldn't be a problem locating the info even if you do not use any image editing/management software (which is very rare considering every camera comes with some form of software other than the driver).
If I'm not wrong, for pictures posted on internet forums, if you just use your windows XP, you need to save the picture in your HDD/storage device before you can check on the EXIF.
I find this troublesome and therefore have installed opanda so that when I see pictures posted in internet forums, all I need to do is to right click on the picture in my internet browser (such as IE or Firefox) and view the EXIF directly without needing to save it into my storage device (although the picture is actually in my internet browser temporary folder).
For your own pictures already saved on your storage device or internet pictures saved on your storage, you can of course just use the Windows XP and check the EXIF from the picture's properties.
Opanda in action (viewing the EXIF of a picture posted in clubsnap forum) :