URL variables do not make much sense.
I would normally just do something like this...
aPage.cfm
<cfset variables.thisPage = "aPage">
menuInclude.cfm
<cfif variables.thisPage = "aPage">
<img src="/images/aPage.gif">
</cfelse>
<a href="index.cfm"><img src="/images/a_home2.gif" onmouseout="SwapHome()" onmouseover="SwapHomeOver()" name="image1" / border="0"></a>
</cfif>
<cfif variables.thisPage = "bPage">
<img src="/images/bPage.gif">
</cfelse>
<a href="index.cfm"><img src="/images/b_home2.gif" onmouseout="SwapHome()" onmouseover="SwapHomeOver()" name="image2" / border="0"></a>
</cfif>
There are innumerable variations on this depending on how exactly you want your menu to work but this gives you the basic idea.