Well, IE 7 is in rapid decline. MS has made IE 8 a priority update. So unless you never update your computer, or do and specifically refuse to update to IE 8 despite dire warnings from MS, you use IE 8 or greater.
So, you could just skip support for IE 7. You might want to use a meta tag to force IE to use the latest version engine and standards available:
It should be the first meta tag on the page before any scripts or styles. It prevents IE 8 and greater from using compatibility mode (IE 7 engine optional standards of 7 or the browser's top standards), even if the user has that or full IE 7 mode (IE 7 engine IE 7 standards) switched on in their browser.
<meta http-equiv="X-UA-Compatible" content="IE=5, IE=8, IE=9, IE=10" >
Now it's possible to use 2 or more versions of jQuery on a page. But that can get tricky and depends upon all the jQuery code on the page 'knowing' which version it's using. If using just 2 versions, one of them has to be set in noConflict mode and all of the jQuery code that uses the noConflict version must be capable of running in noConflict mode and be setup visa vis its use of jQuery before the other version of jQuery is introduced to the page. Some scripts that can run in noConflict mode cannot run with another version of jQuery on the page though because they might reference jQuery as jQuery either literally or as part of a method after the second version is introduced.
That said, the dropline menu looks like it will run well in noConflict mode. To test it out:
//build menu with DIV ID="myslidemenu" on page:
<!-- your script that use version 1.7.1 goes after here -->