Well, right clicking the picture requires something to display the picture. Don't ignore that click. That is simply a file association function.
If I associated JPG files with Microsoft's "Picture Manager" (A built in component of Office Pro 2007), and click on a picture - it opens in that program, and a right click is all that is needed to resize it.
If you use File Association, all you do is click on the image file name and it oipens in Irfanview. (You don't need to open the program. Vista does it for you by association.)
The just click on IMAGE and resize (same menu.) It is really no more steps that XP's Tweak-UI module.
It will also do batches - but that is not recommended. It assumes that all image qualities are equal - and that is rarely the case.