If your old Software does challange an special / old Version of IE, you can fulfill that requirement without another Virtual Maschine by installing IETester.
http://www.my-debugbar.com/wiki/IETester/HomePage
I would loved to had known that Software a bit earlier.
I ran into serval problems in upgrading an Zyxel 2000W Wlan Phone by using Win7 with Firefox 3.6 / IE 7.
I couldn't find the "Browser for Upgrade File" bar, so I tried everything on the net, including Chrome.
In the end, I used an Virtual PC / Windows 98SE(!) which I keep handy for... stuff - and could upgrade the phone.