Verifying in IE

[Lane Brooks]

I developed a simple registration web page for a non-profit fundraiser. 
I have a virtualbox installation of windows xp that I run out of linux 
to check functionality on IE, but I have only been verifying in IE8. I 
just received word of a user having problems on IE7, though. My page is 
pretty simple, so I thought I was safe from needing to figure out how to 
install different versions of IE for testing, but now it looks like I 
need to. Given that web development is not my area of expertise and 
given that it has been probably ten years since I have used windows more 
than just occasionally, I was hoping people in the area of web 
development could offer insight on how to install and test with multiple 
versions of IE.

 From my google searches, it seems different versions of IE cannot be 
co-installed, but I have found sights offering executable downloads that 
supposedly include all the IE versions. They seem more like Trogan 
Horses to me. Other sites seem to indicate you need to use a different 
virtual machine for each version of IE you want to test with. If that is 
the case, I can clone my current virtual machine, but then how do I 
downgrade IE? The information I get from googling is contradictory and 
hard to know who to trust. Is there not some sort of Microsoft issued 
developer package with all the versions of IE that you can co-install on 
one machine? If not, how do Microsoft employees verify their web pages 
across their multiple browsers?

Thanks,
Lane