At the moment I use emacs 22.1.1 with the vc-mode. The following steps are necessary to get Emacs vc-mode working under Perforce.

• Download the lisp files p4-lowlevel.el and vc-p4.el written by Jonathan Kamens from Perforce
• Add a file P4CONFIG.txt to the root of your local perforce workspace directory. Do not check in this file into Perforce. The file P4CONFIG.txt contains your connection parameters to the Perforce server:
  

  P4PORT=<perforce server name>:<port number>
  P4USER=<your perforce username>
  P4PASSWD=<your password>
  P4CLIENT=<your perforce workspace>
  

• Add the following lines to your .emacs file:
  

  (load (expand-file-name "e:/emacs/perforceIntegration/p4-lowlevel.el"))
  (load (expand-file-name "e:/emacs/perforceIntegration/vc-p4.el"))
  (require 'vc-p4)
  

• Add the files p4-lowlevel.el, p4.el and vc-p4.el to your emacs installation in for example directory "e:/emacs".
• Add environment variable P4CONFIG as "P4CONFIG.txt", so without the path name.

Now you can add, check out and check in from emacs with the command vc-next-action (C-x v v).