Hi and welcome BlueTiger.
This converter does not exist.
For your members you can use the Batch Import of Users function in Geeklog admin section.
You can import a batch of users into Geeklog. The import file must be a tab-delimited text file and must have the fields in the following order: full name, username, email address. Each user you import will be emailed with a random password. You must have one user entered per line. Failure to follow these instructions will cause problems that may require manual work so double check your entries!
Manualy you will need to create your forum categories and for the posts you will need to write our own function to import them.
I'm available to customise your themes or plugins for your Geeklog CMS