What is the difference between compaq presario v6221tu and compaq presario v6221eu

There may be no difference, except maybe language settings.

They could be localization codes, such as EU could mean Europe.

They could be OEM codes, such as models sold in Best Buy stores in the US or maybe North America, etc.

I think the TU is only available through HPshopping while the EU is a retail model. This means the TU has different configurations.