A good place to start from would be here http://www.microsoft.com/learning/mcp/mcts/default.mspx. From there it all depends upon what certification you are planning to take: You can get certified either on MOSS or in Windows SharePoint Services 3.0.
Keep in mind that practical knowledge is essential for all these exams and if you have done couple of implementation, you will find these exams a lot easier. An easy way to get hands on experience is to download the MOSS trials or even preconfigured VHD's from Microsoft: http://www.microsoft.com/downloads/details.aspx?familyid=67F93DCB-ADA8-4DB5-A47B-DF17E14B2C74&displaylang=en
The Best Cheat Sheet (that have found so far) is go to these URL's and Check the Skills Measured Sections and start implementing these concepts in your project and keep practicing.
Check these URLs for Skills measured, Reference Books, and Practice Tests:
The certification path and preparation guides are available at the following URL's:
MCTS: Windows SharePoint Services 3.0, configuring http://www.microsoft.com/learning/en/us/exams/70-631.mspx
MCTS: Microsoft Windows SharePoint Services 3.0 – Application Development http://www.microsoft.com/learning/en/us/exams/70-541.mspx
MCTS: Microsoft Office SharePoint Server 2007 – Configuration http://www.microsoft.com/learning/en/us/exams/70-630.mspx
MCTS: Microsoft Office SharePoint Server 2007 ― Application Development http://www.microsoft.com/learning/en/us/exams/70-542.mspx
Another thing to note is that Microsoft announced SharePoint Master Certification. This Certification path would get you SharePoint Architect or SharePoint Certified Master Credentials.
More details can be found here:
Plus, I think currently you can receive up to a 50% discount.
A for a few SharePoint 2007 Exams tips check out this site:http://www.sharepointforum.com/en-US/Blog/archive/2007/11/20/the-sharepoint-2007-exams-tips.aspx