The sticker on the drive has the firmware version on it. Top right, it will show something like: FW:029G.
The default firmware is listed on the label. Once installed (assuming windows), you can see the firmware under Everest Ultimate (Storage->ATA). Or under Device Manager check the properties for the drive, on the "Details" tab, look at the "Hardware Ids".
Something to also consider is if the sticker's are accurate. I mentioned on a different thread that an update tool showed firmware 0956 even though my sticker shows 8820. I'm not sure what that's about yet... I'm hoping the next firmware update will be able to fix that for me.
This utility also reports firmware 0956 on my x18-m: http://www.snapfiles.com/get/hdtune.html
Aside from looking at the label, free software such as HD Tune and Crystal Disk Info show firmware installed.
I created another thread about a pre-production firmware on my X-25M 160G Postville: http://communities.intel.com/message/76261#76261
I have firmware version 0953 on it, and can't update to the latest firmware either.
What the hell is going on here?!