Hi Chaos,
I haven't looked at any of the "other" posts that you are referring to, but I'll throw in my 2 cents worth. The only problem with your approach is (like you mentioned) it relies on there being a "." in the file name. Most of the time this will be okay since most files have a ".ext", but not all files have extensions. For this reason, I attached a VI written in 7.1 that reverses the string and then searches for the first "\". It then reverses the string back to make the relative path. I can't think of any circumstances where this would back fire (I can't think of any circumstances where there wouldn't be a "\" in the path).
Hope this helps!
Travis H.
National Instruments
Travis H.
LabVIEW R&D
National Instruments