If VS2005 is only installed on your PC, you just only install XPacSDK_CE_n.n.n_VS2005.msi.
Correspondingly, install VS2008 only and only install XPacSDK_CE_n.n.n_VS2008.msi.
Both of VS2008 and VS2005 are installed on PC and recommended you to install XPacSDK_CE_n.n.n_VS2008.msi.

Note: n.n.n is sdk version number