Question: I'm trying to use R through SPSS syntax (I'm using SPSS 18 on windows 7) which requires installing a special plugin: PASWStatistics\_RPlugIn\_1802\_win32.exe. Also I had to install an older version of R(2.8.1 - required by my older version of SPSS - i like it better than the new ones). The plugin now works, R (both versions) works, but Rstudio stopped working and won't start even after uninstalling and re-installing.
Does anyone have any similar experience and could suggest a solution?

Answer: 
The following link specifies how you can configure Rstudio to work with a specific R version you have installed:

<http://www.rstudio.com/ide/docs/advanced/versions_of_r>

Just install R 2.8 and 2.14 and let spss use one, and Rstudio another. 

You are taking a risk by using old versions of spss and R (bugs that have been fixed in newer versions, decreased performance, possible incompatibility with other software e.g. R packages, missing functionality).
You can have multiple versions of R installed at the same time - I have five. The current version of Statistics, 21, goes with R2.14. I don't know how Rstudio determines which version to use. You might need to reset the R environment variables or your path settings.