Hi,
First of all, SQL Server 2012 can handle 2005 databases easily (as Kornfeld already said this). But if you need SQL Server 2012 and 2005 instances running on the same operating system (because of backward compatibility or other reasons), then I can say this:
1. If your operating system is
Windows Server 2012 or Windows 8, then the answer is maybe. Why? According to Microsoft: "SQL Server 2005 (the release version and service packs) and earlier versions of SQL Server are not supported on Windows Server 2012 R2, Windows Server 2012, Windows 8.1, or Windows 8."
But I have seen some workarounds for this (I haven't tried them). Links:
a.
Install SQL 2005 Developer on Windows 8[
^]
b.
How to install SQL Server 2005 Express in Windows 8[
^]
2. Well, if your operating system is
not Windows Server 2012 or Windows 8, you can do that. Microsoft confirms that if you have installed SQL Server 2012, you can install SQL Server 2005 and run them side-by-side. SQL Server 2005 and 2012 instances can run at the same time and I can confirm that from my own experience. In your case, you may get some error messages during installation. If that would happen, you need to deal with them.
By the way, I would advise you to install SQL Server 2005 database engine only and use SQL Server 2012 Management Studio to manage both instances (2012 and 2005).
Please let me know if you need further help.