I have created a new lightweight image resizing tool. You can download here:
http://www.wildfisher.co.uk/specials/wffresizer2.exe (http://www.wildfisher.co.uk/specials/wffresizer2.exe)
It's only 1.6MB
No install required. Just run it. You can open the file you want to resize or just drag it onto the running resizer. It will resize it proportionally to a maximum width or height of 640 (it can be set to any value) which ever is the greater dimension will be 640px after the resize, thus it handles landscape and portrait formats sensibly. It will be saved back to the original directory under a new file name - prefixed with wff and the date and time at that instant. It is thus impossible to overwrite any existing files. So, for example, if you drag and drop from the desktop the new file(s) will appear on the desktop.
Do not run it "as administrator" under windows 7 or Vista, it won't work if you do.
It supports jpg and png and always "stays on top" when running so you don't lose it under a load of other windows.
It also works with multiple files in drag and drop mode. That is if you select and drag - say - 6 files onto the resizer it will do them all in one go. :8)
Simple.
I have added a tutorial video on how to use this in the FAQs
http://www.wildfisher.co.uk/smf/index.php?action=faq;sa=show;faqid=8 (http://www.wildfisher.co.uk/smf/index.php?action=faq;sa=show;faqid=8)