IIS 6 and IIS 7 are both types of windows hosting. IIS 7 is the more up to date version and as a result has better support for php based websites. IIS 7 also offers support for ASP .NET 4.0*.
Even if your website was developed with asp code for IIS 6 you can change your settings in IIS 7 hosting packages, so that your code will run the same as in IIS 6 in http://cp.blacknight.com under:
Websites > domainname > Website Configuration > IIS Application Pool > Change it to "Classic" mode
You might need to make sure your Windows subscription is selected in the Subscription drop down menu first if you have multiple subscriptions.
*ASP .NET 4.0 support only available under Windows 2008 plans running in 'Integrated' mode. Please submit a ticket on the right or contact firstname.lastname@example.org to request we enable this for you should you need it.