Installing Windows 7 on a network

First of all I would like to apologise for the lack of information I can provide at the moment.

My situation is a friend of mine asked me to help with some IT problems he has at his business.

The situation is the wages software they are using has warned them that in 3 weeks time it will no longer work on Windows XP and they need to upgrade the OS.(I have already informed him that his network is at risk because they are running XP and is no longer supported)

I know all the computers at his business (10 PCs) are all running XP, are connected to a server and running on a network (not sure what server software they are using probably Windows NT or Windows Server). My question is will I be able to install Windows 7 on just one of the PCs? Will I be able to install Windows 7 using the installation disk?

Thanks for any help you can provide and let me know if you require further information and I will try and provide it.