Old Plug-ins

How can you workout if a plug-in that was designed for a previous version of Zen-cart will work with the latest versions?

adb34:

How can you workout if a plug-in that was designed for a previous version of Zen-cart will work with the latest versions?

There's no 'easy' to work this out, because there are a number of factors involved, such as, does the add-on create new configuration options in the admin menus? If so, then the'll need to be updated to support the current way of doing this.
Do the addons use old/obsolete PHP code? If so, they'll need to be updated to suit the newer PHP versions.
Do the addons modify any of the zenCart core code? If so, they'll probably need updating.

If none of the above is applicable, then the add-on may work without any changes needed, HOWEVER, most of the 'popular' add-ons have already been updated for V1.5.x compatibility, so you may be better of asking about the specific add-ons that you are refering too.

Finally, you can always make a back of your site, install the add-on's and see if it works or not. If it doesn't, just restore the site from the backup with the knowledge that the add-on isn't compatible.

Cheers
RodG

See if there is a support thread, as the vast majority of plugins have support threads or at least queries about them, chances are that someone else will have asked the same question

Thank for the help :)

Easiest way is to just download and upload to a test site.