In Excel 2007 you can also use Conditional formatting:
Select the cells you want to change.
In Conditional Formatting, choose "new rule"
Under "Rule type" choose "Format only cells that contain"
Under "Rule description" choose "Cell Value", "between", "0", "9999999" - you can of course tweak these values according to your requirements.
Click on [Format], and then on the Number tab, choose "Custom", and in the Type box, overtype "General" with ""88"0" (i.e. it should contain "88"0).
This is in some ways the same as the previous answer, but it will do it in place, without having to create a new column. Note however, the actual value in the cell will not include the "88", so if you subsequently want to copy or use the data in the cells, (besides plain vanilla copy & paste which will also replicate the conditional formatting) many methods will NOT include the "88" prefix.