FitNesse doesn't allow carriage returns in test fixture table. Normally, I replace carriage returns with a comma (or some other sentinel value) and pass it back to FitNesse. I noticed a posting on the FitNesse email group that recommended defining a variable and then using the variable in the table.
An Example:
!define multiLineAddress {Gifford Consulting
Attn: Tim Gifford
123 Main Street
Des Moines, IA 50266}
!|Check Address|
|Address|
|${multiLineAddress}|