Well actually I don't use IRFanView but I found a nice FREEWARE thumbnailer today that has nice features and does a great job, it's got a 100% positive rating on CNET.
I use an old registered copy of Express Thumbnail Creator which overall kicks ass except I'm never happy with the thumb quality, so I'm going to try this free one for awhile.
Check it out, not bad for free
http://download.com.com/3000-2192-10...ml?tag=lst-0-1
Nedder