You can upload into the Member Albums on this site. It will resize the pictures and automatically create an album for you (if you don't have one there already).
Each picture you upload will also include the code you can use in forum posts to display your pictures.
Using other sites, like PhotoBucket, is also a worthwhile option but I can't guarantee that I'll always support them.
If you prefer to upload the pics as attachments, and you don't have any sort of image-editing software, below is a link to Microsoft's site with a free solution (choose the Image Resizer):
http://www.microsoft.com/windowsxp/d...powertoys.mspx