The question here is more along the lines of “Do you have a RAID controller” than anything else!

Using the operating system (Windows) you can create a RAID 0 drive using the Disk Management MMC, but this dumps an awful lot of system maintenance work on the system processor (all the RAID and metadata calculations are performed by the OS) and you will most likely not gain much (if any) additional speed by setting up this RAID 0 array.

If you have a RAID controller (either built into your system board or as a separate add-in card), let me know – I can gie you some generic (if not sep by step) instructions on what to do…

Sorry for the lack of info, I have a built in Intel ICH9R SATA RAID controller. However I did some checking online and found a blog from another xps 420 owner and they tryed to do the samething “using the eSATA port” and looks like they ran in to a issue. They had to reinstall there operating system “and I am not sure why” to get the e-SATA port to work. I pluged mine in and it would not work I tryed a USB connection on the drive and it worked fine. I am not sure what this person met by reinstalling there operating system to get it to work as I have already reformated my system drive and upgraded to Vista Ultimante 64bit and mine still dont work. The link to the blog is: http://blogs.technet.com/keithcombs/archive/2007/12/15/dell-xps-420-first-impressions.aspx
Any other info you may need let me know and thank you for the help.

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Running multiple hard disk drive could be effectively done if there are similar storage devices. It is better not to use your external hard disk drive as an internal drive because it might create conflicts or incompatibility issues later on.