" Have Version 1.03 german. Can I install version 1.14 english ?"

 

As long as you don't mind the English BIOS screens then it isn't a problem.

 

"Must I make an update to 1.14 before I switch from Windows XP to Windows Vista Premium Edition ?"

 

It wouldn't hurt to install Vista with the latest BIOS version already in place although it isn't required.  In checking the BIOS history I don't see anything Vista related in the later BIOS releases.

Run the Dell Vista Readiness scan.  If there is an issue with the BIOS version it will be flagged.

 

http://support.dell.com/support/topics/global.aspx/support/vista_support/en/vista_readiness?c=us&l=en&s=gen

 

I have an E510 (same as the European 5150) and with the A05 BIOS it was flagged as an issue.  I upgraded to the new A07 BIOS for this machine and ran the Dell Vista upgrade scan and it no longer showed the BIOS as an issue.