Excel 32 vs 64 Bit
In terms of using SummaryPro the version of Excel that you are using makes no functional difference. The only difference is that if you have the 32 Bit version you have the option of using the "32 bit only" version of SummaryPro which doesn't install an .exe file as part of the licence, making it easier to install in many corporate environments.
Excel 2007
This is always 32 bit
Excel 2010
Select the File tab on the excel ribbon and then select Help (or simply press the <F1> key. The bit version will appear under the About Microsoft Excel heading.
Excel 2013 onwards
Select the File tab on the excel ribbon and then select Account and then About Excel. The bit version will be displayed in the top line of the dialogue that then displays.