when installing a mod should i take the files for the particular mod from the default theme and copy them all in the other themes that i also want to use??
The install package for simpleportal offers you the ability to modify just the default theme, or to modify all the other themes at the same time.
Most of the time, this option will work just fine.
But if your other themes are VERY much different from what the installer expects, it won't find the right place to make the changes, and it won't do them.
Make a list of all the "test fail" details, and then you'll need to figure out how to make the changes yourself (if you want them).
For the new files modifications are adding; you don't need to copy the template files to other themes than default theme. SMF "fallback"s to default theme files if it can't find the files needed in the custom themes. And it's a lot better to have them only in default theme directory to avoid such issues during upgrades:
http://simpleportal.net/index.php?topic=10077.0
Thanks guys :D