I wouldn't recommend doing OSCP plus another cert at the same time if you are new to pentesting.

OSCP is a very challenging course and exam and really makes you try harder and is not to be taken lightly.

I saw some people taking OSCP and later CEH with great confidence.

Be aware that you will get the most accurate information from the BackTrack course, and other alternatives sources they may refer to compared to (almost) any CEH courseware. I've recently done a lot of the modules for fun (pretty much all of them at a prep material provider), and the cryptography part along with others were nice, but others were very (and extremely) poorly described.

Especially the web application security parts, among others, they just gave you a brief overview, not the actual knowledge that may be required when you do PWB and OSCP, or for that sake exploit development, vulnerability research, in-depth black box penetration tests, etc.

It's just some good advise so you don't end up being more confused. When it comes to buffer overflows, there's two major tutorials that are very old, yet still a bit useful. Keep in mind that different operating systems, function differently.

Buffer overflow references:
http://insecure.org/stf/smashstack.html
http://www.cultdeadcow.com/cDc_files/cDc-351/

Even I (had fun but trouble too) developing my first buffer overflow (from a known exploit) once too:
http://guides.intern0t.net/msf2.php (It's a video guide and it goes through almost the entire process)
http://en.wikibooks.org/wiki/Metasploit/WritingWindowsExploit

And of course not to never forget, Corelan:
https://www.corelan.be/index.php/articles/ (look under Exploit Writing Tutorials )
E.g.: https://www.corelan.be/index.php/2009/07/19/exploit-writing-tutorial-part-1-stack-based-overflows/
http://www.corelan.be/index.php/category/security/exploit-writing-tutorials/


All of these, are some of the best tutorials and references on the Internet.

You can probably find some guides on securitytube.com as well 

Enjoy!