Thanks for you reply Graynomad. I don't believe everything that is said in a forum, but i always do research about anything that might be an issue concerning my case. In fact, other than that forum, I couldn't find anything about the I2C and SPI sharing the data bus, so that's why I decided to post something here, to get some opinions.
With regards to the code, it could be that I have some errors but I kept the code quite similar to that on the SD library examples but it definitely needs some more work. I am currently not at home so I can't post the code but if I fail in making it work, i will definitely do so. At least now i know that i might have a chance of solving it software wise.
Thanks again.