> Examples:
> foo.com/blog.php?mod=comment&id=1102023563
> foo.com/blog.php?mod=comment&id=1098503488
> foo.com/blog.php?mod=comment&id=1089606282
> Of course what I'm really after is the number that appears
> after id= , eg 1102023563. Do I understand correctly there
> is no way to get it save the file as 1102023563.html or
> something similar?
You can:

Set options / Build / Options
and enter:
%h%p/%n%[id:-:::].%t

The %[] syntax is:
%[param:before:after:notfound:empty]

param: the query string parameter name
before: what to put before, if found
after: what to put after, if found
notfound: what to put, if the parrameter is missing
empty: what to put, if the parameter is empty