Is it at all possible to do a software RAID0 (with Ubuntu Server, installing Crunchbang on it though) with drives of drastically different sizes? One of the drives is 250GB while the other is 60GB.
With Ubuntu software RAID, the partitions should be the same size or close to it, because it's a multiple of the smallest size, and any extra will be unused. So you can create a 60GB partition on the larger disk and end up with:
You can mount one volume as
Whether software RAID-0 is worth it is another matter.
Not "raid 0" in the strict sense without losing a lot of capacity.
Have a look at LVM, the Logical Volume Manager: https://help.ubuntu.com/community/Installation#LVM%20Installation%20Guides
... perhaps you'll find something in there.
Another option is to just RAID0 the small drive and part of the big drive. Leave the extra room on the big drive for bulk storage.
Linux software RAID (any level) works at the partition level rather than the device level, so you could create a 60G partition on each drive and RAID0 them into a single 120G array.
However, unless you have specific performance needs which require higher data transfer rates and you've tested this to verify that it gives a significant boost over a regular, non-RAID0 partition on a single drive, you probably don't really want to do this since, with the drives in question, you can easily create a 120G non-RAID0 partition on the larger drive which will give you the same capacity and more security for your data. (With the plain partition on the larger drive, you lose your data if that drive fails. With the RAID0 partition striped across both drives, you lose your data if either drive fails.)
 If you really wanted to, you could probably make one 60G partition on the small drive, four 60G partitions on the large drive, and combine them all into a 300G RAID0 array, but that would be a purely "because I can" project, given that it would not only have the reliability issues of RAID0 in general, but it would also be very slow to RAID multiple partitions on the same device together.
 Or maybe not. Given the interface of Linux software RAID, it seems like it should allow you to combine multiple partitions from a single device, but there could be a sanity check in there somewhere that disallows it. I've never been inclined to try it myself, so I don't actually know whether it's allowed.