I need to re-organise some data from Excel .. just some fairly basic re-grouping and re-summarising the data in a slightly different format. Are there any linux apps that could help me?

Sure. If you want to stay in a spread sheet, the calc program in OpenOffice.org. If you want to use a data base management system, say, MySQL, save the spread sheet as a CSV, define a schema and load the stuff. If you just want to fiddle with text, save as a CSV, write a little two-line or so AWK program and there you go.

The possibilities...

More specifcally, I would like the final result to summarise the data into just one row per RFI number and look something like this .....
RFI-000008 Re: Dimension Check - Turner 2/5/07 - Davidson 3/5/07 - Marina 3/5/07 - Aru 4/5/07 - Aru 8/5/07
RFI-000007 etc etc

This is the core data ...

RFI*SUBJECT*Date*ORG
RFI-000008*Re-Dimension Check*2/5/2007*Turner
RFI-000008*Re-Dimension Check*3/5/2007*Davidson
RFI-000008*Re-Dimension Check*3/5/2007*Marine
RFI-000008*Re-Dimension Check*8/5/2007*Aru
RFI-000008*Re-Dimension Check*4/5/2007*Aru
RFI-000007*Re-Beam Size Confirm*4/5/2007*Sampter
RFI-000007*Re-Beam Size Confirm*4/5/2007*Marine
RFI-000007*Re-Beam Size Confirm*5/5/2007*Aru
RFI-000007*Re-Beam Size Confirm*7/5/2007*Davidson

That's the kind of thing I'd do with AWK, maybe a C program, maybe MySQL depending on the amount of data and for how long I had to summarize the same stuff over time. I'd probably start with AWK (because it's easy) then move on to MySQL if I had a large volume of data to contend with. It's a pretty straight forward proposition; couple of if-else's and away you go.