Deploying Code to use in functoids.

I am new to BizTalk and I have just started working for a company that uses BT to do EDI work. Basically I am doing alot of work in the mapper between different schemas. I have a situation where I would like to use some c# code and according to what I have read from Msoft you can do this by creating a class library and referencing it from your BT maps using the scripting functoids to grab from the external assembly. This is also shown in the "Extending Mapper" sample provided with the SDK.

The problem is that in both my case AND in msoft's example, BT errors out on map test and tells me that the c# assembly is not referencable and suggests it might need to be deployed in the GAC. I tried this, however, it seems that only BT assemblies are eligible for the GAC, not c#. So my question is, How to I make that c# code referencable. Msoft says it can be done, but I can't figure out how that actually needs to happen. Any ideas? Thanks.