Numbers, decimals...help!

Hi,
I have a program with six text boxes and a few of these relate to one another ie. data entered changes the data in the other after a calculation. The problem I am having is that if I display a negative num or decimal or nothing...I get an error.
I tried some code that checks to see if it is a number before doing the calc but it didn't check for decimals and negative numbers.
Can anyone please help with how to do this.

Thanks in advance,

Scott

Here are two functions that will check the numbers

public Function CheckNeg(vValue as single) as boolean
if abs(vvalue)=vvalue then
CheckNeg=false
else
CheckNeg=true
end if
End Function

Public Function CheckDecimal(vValue as single) as boolean
if Int(vValue)=vvalue then
CheckDecimal=False
else
CheckDecimal=True
end if
End Function

These Functios will both return false if the number is OK, else they will return True if the number is a decimal or negative

PS If you use singles instead of Integers or Longs then unless you are doing square roots then you shouldn't get many errors