Start in safe mode (repeatedly press F8 at startup) and log as "administrator". Leave the password field blank if you didn't set any.
Run windows explorer (winkey + e) and select the root of c: in the left pane. Go to tools => folder options. In the general tab tick "use classic folders". In the view tab untick "hide protected operating system files", untick "hide extensions for known file types", tick "show hidden files and folders". Click apply to all folders then ok. Back in windows explorer click on view and select the details view. Browse to c:\documents and settings\yourusername\my documents\ and see if you can find the folder.
If you still don't see the folder search for one of the files that was in the folder using start => search => files and folders. Tick the first 3 boxes in the advanced section. Right-click => properties on the search results to find the path of the file.
I just created an alt+255 folder like you did (in c:\temp\) and I hid it. When I went to start => run and typed c:\temp\ \ (the blank space is alt+255) I was able to access the folder and the files in it. Attrib and ren from the cmd prompt worked too (c:\temp\attrib " " -h, the other parameters are not needed if the folder only has the hidden attribute, if you set it as read only as well then use -r -h).
A program like windirstat (freeware) might help :
http://windirstat.info/
Or totalcommander (30 days shareware) :
http://www.ghisler.com/download.htm
(go to Configuration => Options => Display => Show Hidden/System files)
here's what I see with total commander (click to zoom) :