You'd just need to slot the google code into another file (eg page.asp) then include it in where you want it to show - the site integration mod would be an easy way to do that.
look out for the google t&c's tho... don't they say something about putting the ad's on thankyou pages etc?
if its any help the code i use around mine to stop them appearing on post_info.asp etc is:
if (Instr(Request.ServerVariables("Path_Info"), "default.asp")) OR
(Instr(Request.ServerVariables("Path_Info"), "forum.asp")) OR
(Instr(Request.ServerVariables("Path_Info"), "topic.asp")) OR
(Instr(Request.ServerVariables("Path_Info"), "post.asp")) then
%> <!--#INCLUDE FILE="file.asp" --> <%
end if
There's probably some pages I've missed out, but it's pretty straightforward on how to expand on that...
--->afterthought... you could change it so that the files listed are those you don't want the ads included on so it looks something like:
if (Instr(Request.ServerVariables("Path_Info"), "post_info.asp"))
'Copy and paste, replacing post_info.asp with other files to be omitted
then
'skip
else
%> <!--#INCLUDE FILE="page.asp" --> <%
end if
obviously theres some other files youd also need to block as well as post info... hope thats some help to ya.