Number Validation

I have a text filed and on submitting the field I just want to check to ensure it is a number.

Either floating point or integer.

"12.9", "10000"

Hmmmmm

I'm and idiot, I know.

Use a CompareValidator.
Set the Operator property to DataTypeCheck
Set the type to whatever you need, probably double or currency.

Or you could use the IsNumeric function, but Hellswraith's way saves a trip to the server, by doing it client-side.