my default %TEMP% is set to "c:\Documents and Settings\Кирилл\Local Settings\Temp\"
That's because my locale is cyrillic russian and temp path contains full account name as it's set.

So running
>ruby rubyscript2exe.rb main.rb
results in 
rubyscript2exe.rb:369:in `mkdir': No such file or directory - c:/DOCUME~1/КИРИЛЛ/LOCALS~1/Temp/tar2rubyscript.d.2452.1
(Errno::ENOENT)
        from rubyscript2exe.rb:369:in `extract'
        from rubyscript2exe.rb:598

That can probably be a result of Ruby's externals being fully unicode-oriented, while IO in Windows is using CP-1251.
I've dirtily overcame the problem setting %TEMP% var to "D:\Temp".

After all, thanks for the great script. (And I know my English-writing skills lack practice:-/)