Add a webcounter - in what file ?

If I want to add a webcounter like this one -
http://www.google.com/analytics/index.html

Where should I put the webcounter-code ??

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My Gallery
www.photo.box2600.dk

Gallery version = 2.1.2 core 1.1.0.2
PHP version = 4.3.10-18 cgi-fcgi
Webserver = Apache/2.0.54 (Debian GNU/Linux)
Database = mysql 4.1.11-Debian_4sarge7-log, lock.system=flock
Toolkits = ArchiveUpload, Exif, ImageMagick, NetPBM, SquareThumb, Thumbnail, Gd, Getid3
Acceleration = none, none
Operating system = Linux web1 2.6.8+vserver #1 SMP Wed Jun 7 23:09:25 CEST 2006 i686
Default theme = PGtheme
Locale = en_US
Browser = Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.3) Gecko/20070309 Firefox/2.0.0.3