|"But It converted ALL my scanned files to Irfanview"|
What does that mean? Irfanview is viewing software, not a file type. If you don't have the file extensions enabled in XP, turn them on so you know which file type you're working with. The red Irfanview icon is the program association, not the file type. If you accepted the default settings when you installed it, all image files (jpg, bmp, gif, etc) will now open with Irfanview when double clicked on. Rather than double clicking, try right clicking then highlite "Open With" & you'll find other programs such as Paint, Windows Picture & Fax Viewer, possibly others.
Regardless, the Irfanview program has nothing to do with your problem posting to Facebook. If for some reason you want your photos contained in a word doc, just open Word, then either drag the image file into the word doc, or copy/paste the image file, or use the Insert feature.