External Hard Drive for both 360 and PS3

I'm needing to buy an External Hard Drive for both my Xbox360 and PS3. Is it possible to partition an EHD to allow both system's formatting? I'm looking to just swap USB connections between the systems for the shard EHD, if possible. 500GB, 250 per system; is this possible? Thank you in advance.

It'll work for the PS3, not for the XBox. The XBox will only use, I think, up to 32 gigs of anything that isn't an MS made for 360 HDD.