How do I turn my Dell Precision 530 into a server without losing XP?

This is an older computer of mine that is built to be a server, but currently only runs XP Pro. Due to some complications I cant uninstall Windows XP, and last time I tried dual booting Ubuntu I got Grub Rescue. What is the best way to turn my computer into a server without affecting the current install of XP? Also, what benefits can I gain from making this computer a server?How do I turn my Dell Precision 530 into a server without losing XP?
XP Pro is fine for almost all server activities.

Server is a fairly ambiguous word as it can define hardware and/or software and (in the case of software) be local or remote. Also a server can be dedicated - that is performing one task only - or can perform multiple tasks.

The tasks you want it to perform really define your server. There are several broad categories:

File Server: This is where files are stored that can be shared on client machines. This allows centralisation of work whilst reducing storage burden on client machines. A simple way to achieve this is just to share folders with network users. Specific examples of this would be an FTP server or media server.

Authentication Server: The server acts as a secure entry point for all PCs on your network. This is a key use for servers in the corporate/academic world, but isn't normally needed in the home. Microsoft's standard terminology for this is a 'domain controller', but this isn't an option for XP Pro as only server operating systems can fulfil this role (such as Windows 2003 Server). That said you can use other open source LDAP software to achieve a similar end on XP.

Service Provision: This is where your server actually does some decent work (the above tasks are very light on CPU usage) to take some strain off of the clients. Examples of this are Web Site/Application, Database Server, Online Game Server or Rendering/Printing. Achieving this on your PC is dependent on which you want to do, but most involve installing software (although XP Pro can use it's own IIS to provide Web Sites, it's deliberately limited to just 10 users).

Backup Server: Simply backup your important data folders across the network such that even if your client PC totally blows up, you still have a copy. This is an increasingly important role given that data now readily exceeds the capacity of affordable, writable DVD discs. Again some simple network shares can help achieve this.

There are probably other examples that I can't think of right now.

Turning an older PC into a server is good fun (I've done it myself, of course), but I'm not convinced of its true viability for most tasks. As a file server, the older PC probably has smaller disks than the clients, so there's a bit of a "tail-wagging-the-dog" mismatch there. As a video rendering server, whilst it frees up your client machine, the older processor is usually much slower (and less green) than on your newer PCs - so arguably not an efficient way of going about things either. There are definitely "feel good" rewards in setting up a Web Site or On-line Gaming Server, though these are quite involved (such as needing static IP addresses). Anyhoo - have fun whatever you decide!