Came across this free image resizing app on a photography forum I frequent... I've not used it but some of the members there like it a lot... I post this as I recall an while back someone was looking for a similar free app...

SmillaEnlarger

http://sourceforge.net/projects/imageenlarger/

someone on the same forum also mentioned this one "BD Sizer" as well...
http://bd-sizer.en.softonic.com/download

Like I said I have no experience with these just throwing them out there based upon the opinions of the photographers on the forum at DPReview.com

Cheers

Ken