Some time ago I decided to move my community (worked on Invision Power Board) to Community Server 2007 and create blogs for all users.
But I didn't find any converter software.
So, I wrote converter by myself.
In this project i used LINQ for Community Server MSSQL database and Mysql LINQ Provider for IPB MySQL database.
Several restrictions, such as necessity of additional memory, can be found in this program because of some limitations at the earliest stage of MySQL Linq Provider development.
Because the initial stage of the last and its limitations, I cache all data in Program, so on big database there big memory usage.
What is supported:
- convert all users with unique emails
- Forum structure converting
- Full converting of threads and topics
- Optional. Blog auto-create for each converted user.
What is missed:
- Additional information (ICQ, Yahoo, MSN information)
- User signatures
- Avatars
- Display names (if they turned on in IPB)
- User groups and roles
- Forum permissions
- Attachments
- Voting's
Another restriction for IPB: database must have "ibf_" prefix.
I strongly recommend you to convert forums on local machine.
Conversion of the ~2000 users, ~2000 topics and ~60000 posts took on my machine about 15-20 minutes.
I have published whole solution. You can change the code and use it in any purposes (except commercial use).
I don't grant any warranties and don't respond of data loses. Do backup yourself 
If you have any questions - I will be happy to answer them.
Also will be great if you made some enhancements and share they. May be one day this project will be placed on codeplex.com 
That the link: IPBtoCS_0.0.0.1.zip