Trying to set DefaultValue based on ServerFilter value in ..

I'm accessing two tables using data access pages and framesets. Here's
the scenario:
Two tables, A and B, with a 1 to many relationship between the two (A
has 1, B has 0 to any number of matching rows). The column used to link
the two is called 'intmid' in both tables.
Each of the tables has it's own Data Access Page, and there is one html
file called
'mainpage.htm' with two frames, one for each page. Whichever record you
have from table A, it's intmid value is passed as a ServerFilter to the
other DAP and the corresponding records from table B are shown (one per
page) in the other frame. You are then free to peruse the corresponding
records from table B in the frame.
This works great, EXCEPT when there are no corresponding records from
table B for a given intmid value. In that case, all the textbox fields
in the second frame are blank. When the user needs to add a record to
table B I need to have the intmid field already filled in with the
intmid value from the calling frame.
Ideally, I want to set the DefaultValue parameter for the intmid field
but I can't figure out how to do that. I've been able to hardcode a
DefaultValue, but that's obviously useless to me. I can parse an http
string ("webpage.htm?intmid=value1&whatever=value2....") but
successfully setting the DefaultValue in the called page using this
method has eluded me.
I'm open to any suggestions that involve VBScript, Javascript, or
modifying the Property page for the intmid field. There is no web
server involved here, so anything ASP-dependent is out.
Thanks in advance for any help given.
Regards,
Frank Rustyak