Tested both the 1.5.4 and 1.6.1 on a private desktop with WinXp, SP3. Both run fine. No sign of .Net 3.5 on this machine. So whatever it is, it isn’t the .Net framework. Though it is possible that installing .Net 3.5 fixes the manifest error reported by Dependency Walker.
I dit notice a WinSxS folder containing a lot of manifest files, including many VC++ files. My guess is that on this machine, a different dependency checker is already installed. Probably got it through the autoupdate from Microsoft. So the issue Dependency Walker reports on my laptop is no longer on this machine around.
If anyone else experiences problems like this, try to pinpoint the exact problem and check first with the Dependency Walker tool what it reports before installing .Net 3.5 or anything else to fix the issue.