Here are some simple solutions for IE6:

* http://www.incerteza.org/blog/projetos/shockingly-big-ie6-warning/

Download: http://wordpress.org/extend/plugins/shockingly-big-ie6-warning/

My favorite and what we use on our sites:

* http://www.stoplivinginthepast.com/

Download: http://wordpress.org/extend/plugins/stop-living-in-the-past/

If you need some justfication for why it's time to move on, take at look at these browser usage stats,

http://www.w3schools.com/browsers/browsers_stats.asp

IE6 usage is now under 9% and falling monthly, but I suggest you also check the site's stats to see just many IE6 users are stopping by.

Good luck,

D.K.