sql server 2005 std and i want to upgrade it to 2008 std r2. install r2 on top of 2005 std?

Hi, all friends
I have been using sql server 2005 std and i want to upgrade it to 2008 std r2.
My question is if there may be a problem when i install r2 on top of 2005 std?
Best Regards 
Salih Hanifeoglu

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Salih Hanifeoglu Best Regards