Create a basic custom list with columns:
- Value (type: Number)
- Target (type: Number)
- KPI (type: Calculated. Data type returned from this formula is: Number)
Formula for the calculated column is:
=IF(Value>Target,"<img src='/_layouts/images/KPIDefault-0.GIF'","<img src='/_layouts/images/KPIDefault-2.GIF'")
This will render a nice KPI icon in the KPI column.
(I'd recommend this simple solution because the SP KPI list has had sorting issues at least in SP2007/SP2010 and is a bit heavy if you only need to show a KPI icon based on two columns)