It's totally dependent on which browser, which pluginsm toolbar options (for intstance in IE you can change the buitton sizes), etc...
Figuring in the most common elements all stacked up we found 730x340 to be safe. YOu can go a bit large and be okay many times and in very rare instances it will be too large... but that number is a pretty safe bet 99% of the time.
__________________
Retired Pornosticator
|