I think you should go with Office 2010 even though you dislike the ribbon.
Office 2003 is a delight to use, but any version prior to 2007 will lack support by default to docx, xlsx and pptx formats, which are the current file formats and the ones someone would share with you in the "real world".
Using an older version, even if you install the compatibility pack as someone suggested in another comment, you will experience many issues -- especially in Excel, which was heavily modified (e.g. rows increased from 2^16 to 2^20, new color model replacing the old palette of 16 user-defined colors, new functions such as SUMIFS and COUNTIFS, new implementations for sorting, filtering, conditional formatting etc).
Excel 2010 is almost like 2007, but with many tweaks, corrected statistical functions (they were notoriously unreliable in previous versions) and with improvements to charts which are still almost 100% compatible with the latest version. You should have no problems at all creating and editing documents between Excel 2010 and the most recent version in either direction.
Being an older version of Office, it's also very responsive even on low-end machines -- just be sure to install the 64 bits version.
As for the ribbon, remember that you can double click any tab (for instance, "Data") to automatically hide the menu. You can also customize each and every button on it (right button, "Customize the ribbon").