You should get Windows 7 on the new computer because of the XP already has only limited service available from Microsoft. As reported at Wikipedia:
Quote:
In accordance with Microsoft's posted timetable, the company stopped general licensing of Windows XP to OEMs and terminated retail sales of the operating system on June 30, 2008, 17 months after the release of Windows Vista....
On April 14, 2009, Windows XP and its family of operating systems were moved from Mainstream Support to the Extended Support phase as it marks the progression of the legacy operating system through the Microsoft Support Lifecycle Policy. During the Extended Support Phase, Microsoft will continue to provide security updates every month for Windows XP, however free technical support, warranty claims and design changes are no longer being offered.
Only Software Assurance customers who still run Windows XP can enroll in the Extended Hotfix Support Agreement if they want to receive non-security related hotfixes. The enrollment offer for consumers ended on July 14, 2009.[citation needed]
On April 8, 2014, all Windows XP support, including security updates and security-related hotfixes will be terminated.[2]
However since you apparently have shared software running both on the server and client machines, you should check with all shared applications about running them on Windows 7 and on mixed operating systems. But you need to start planning the eventual transition anyway so this will get you started - and your boss should appreciate you planning ahead.
With Windows 7, I suggest getting 3 or 4 GB of RAM.
I trust you have some process of doing daily end of day backups and offsite storage. But do you backup files during the day in case the HD malfunctions? If not, I would also strongly recommend a RAID 1 system with a redundant HD for constant backups of your critical information as well as the operating system and applications. HD hardly ever fail - but they do.
I had worked at one company for over a year, storing all my personal files on my PC. Finally I asked someone about backups and they said they kept all their files directly on the server which was backed up daily. That made sense so I moved all my files to my private drive on the server. The next week my HD crashed and I would have lost all those files had I not moved them to the server.