Thanks again.
We decided that we will install SAP DB version 7.4 (the same as before).
I downloaded 64 bit installation files and I tried to install it under Windows 7 64bit.
The error has appeared :
The version of this file is not compatible with the version of Windows
you're running. Check your computer's system information to see whether
you need an x86 (32-bit) or x64 (64-bit) version of the program, and then
contact the software publisher.
Can you help us with this ?