I know there are many ways to handle PC naming during deployment, like prestaging, variables, userexit scripts, etc. But a very simple way is to just have the PC prompt you for a Name during The TaskSequece. I wrote a small script that in conjunction wit the fabulous ZTIUtillity.vbs script from MDT does just that.
It is very small and simple script (as I pretty much suck at scripting) so it shouldn't be hard to get it to work. The script will prompt you for a PCname, and write it to sysprep.inf (if needed on VISTA it must be modified to use Unatended.xml instead)
All you have to do, is place it at the end of your postinstall phase and that is it...
I do recommend that you use the Toolkit feature that comes with integrating MDT into SCCM as this will automatically give you assess to all the nice MDT scripts including ZTIUtility.vbs ( juts remember to also add your own script!!)
If you do not know how to get the toolkit part to work try and read my blog entry on integrating driverpaths into SCCM http://kongkuba1.spaces.live.com/blog/cns!EEFF1607E296E5AB!212.entry there is a 6 step guide on how to do this towards the top.
Now for the script:
Copy everything between the === to text File and rename to ***.wsf. That shoud be it.