My apology of not replying in the last few days.....Getting pretty busy with work....Here is my attempt 2...
I am not a particular expert in .NET, so I apologise for not able to give you the full picture on how this could be done.
There is one question to both of you, why are you both using agents? Domino documents and forms could be access directly using URL in specific formats.
I guess both of you just need to know how to get document and open forms using Domino and I think the following is a handy document that refer to how to use different component like forms, views, documents via HTTP from Domino from IBM LDD. The URL is:
It's a bit old and it is only for R5, but I think it should be enough to start and for more details, refer to help in Domino.
chardulce:
- I guess you will need a view create (says "lookup"

with the document key sorted and exist in the first column (e.g. 123). To open the document, all you need to do is:
slpeter:
- I guess you need to use cgi variables to pass the value to the agent. e.g.
If you are opening form directly:
There should be a field call Query_String(hidden) in the form and you could use extract the parameter and put it as a default value in your field, you might need to using WebQueryOpen agent to do that.
If you are using agent:
The parameter will store as context document, you could retrieve the context document by:
Dim session as New NotesSession
Dim context as NotesDocument
Set context = session.DocumentContext
and the field will be called Query_String as well and you could refer to it by
context.QueryString(0)
Hope it helps.
Vincent Liu