niko10000,
Based on your post, there is System.IO.File class of System.IO namespace in mscorlib.dll assembly. This namespace is applied for all the .NET Framework versions, from 1.0 to 3.5.
I never heard of System.File.IO class library in .NET Framework, you can not find the related documents about this class, either. Since you are developing in VB 2005, I would like to provide you the KB 304427 with an example on basic file I/O issue:
How to do basic file I/O in Visual Basic 2005 or in Visual Basic .NET
If you have any further questions, please feel free to reply.
Hope that helps.