do it with the property list editor:

1 info.plist -> contextmenu -> open with -> property list editor
2 change value from bundle version from 1.0 to 1.3 (double click on 1.0 to start edit)
3 click on add item - Paste AIMinimumAdiumVersionRequirement left and type 1.3 right
4 save file and exit editor

sry, got it the wrong way :D
title -> key
1.3 -> string

stupid me, should get more sleep ;)

ok html tags are omitted here. so just do it like the rest in info.plist
the titles should go into "string"-tags and 1.3 into the "key"-tags

CFBundleVersion already exists in original file.

open it with list property editor, there u can't do anything wrong i guess

or open it with editor, and modify/add to get to following result:

CFBundleVersion
1.3
AIMinimumAdiumVersionRequirement
1.3

greets

ty, erterte - works for me!

to edit info.plist: contextmenu -> show package contents
after editing, move your edited skypeplugin to another place (e.g. desktop). recheck that there is no skypeplugin in plugin folder(s). doulbe click it to install the edited moved file. then restart adium.
hope it works.

greets