Self build NAS - Windows or Freenas?

[JayMax]

I've got an old desktop - with an XP licence sticker on the side that I'm looking to turn into a NAS box, with an XFX Revo64 3 port card.
What benefits are there for choosing Freenas over a Windows installation apart from footprint and cost of the OS?
I'm having a play with the freenas VM right now and it seems decent, but if I went for an XP installation (I have a spare 40Gb HDD lying around I can use) then I could use the management software that came with the RAID card?

 

[matja]

... then I could use the management software that came with the RAID card?

Very unlikely, FreeNAS is FreeBSD-based, right?

To be honest, the built-in software RAID is probably far better than the software shipped with most pseudo-RAID cards/chipsets. And you have the advantage that if the RAID card breaks or needs to be replaced, you don't have to replace it with an identical model or reinstall everything using a different RAID format (virtually every card uses different, proprietry, metadata formats)

If its anything like Linux software RAID, you have a great deal of flexibility, like being able to replace the disks with larger models, and enlarging the filesystem, or converting between RAID formats, eg from RAID-5 to RAID-6, while everything is up and running - no need to even close any files you have open on it.