Select Case Question

I have the need to filter out letters put in after a number in a time card spreadsheet. I'm not sure that using a select case is the right approach. I need to allow the user to put in a number and a letter signifying what type of time it is. Each cell equals a date on a calendar. For example if the user puts in 8s then the code will add 8 hours to the total sick time, strip out the s and just leave 8 in the cell. The problem is that I need to deal with all of the other letters/symbols that they can enter. From what I know of VBA which isn't much a Select Case seems to be way to go without using a bunch of nested If statements. Here is what I would like to do but this doesn't work. This is a short example of what I have tried as far as Select Case goes.

Select Case (CellValue)
Case (InStr(CellValue,"s"))
'Deal with s condition
Case (InStr(CellValue,"v")
'Deal with v condition
Case Else
'Deal with all other cases
End Select

I can see a couple of other options but have not been able to find out if they are possible in excel. First an entry filter that would only allow the user to enter specific values would at least limit the letters they could enter. Second being able to strip the letter if there is a letter entered off the CellData entered would make the Select Case much simpler.

Any ideas or other options?

Thanks