Server 2008 comes in 32-bit (called x86) and 64-bit (called x64). Server 2008R2 comes in ONLY 64-bit. Server 2008R2 is based on the same kernel as Windows 7, so it is better to use 2008R2 drivers in the absence of Windows 7-specific drivers, but since you can't install 64-bit on the 2600 and 2008R2 is only 64-bit, then you have to drop down to 2008 and try using the 32-bit/x86 drivers.
No, I'm not saying that you can install Windows 7 on ANY PowerEdge server ... I'm saying that you might be able to, or you might not. It is not supported, so unless someone tests it, there is no way to know for sure.
"some drivers aren't accreted by it"
Not sure I understand what you mean by this.