That should be a Core 2 Duo, not a Core Duo, I remember your boot thread stating a 64 bit OS, not possible on the original x86 Core Duo's. If Core Duo is correct and you actually have a 32 bit system, junk your OS. You can use the 32 bit key for a 64 bit installer of the same product without needing to actually buy a 64 bit version of win7.
If you do a lot of audio and image processing, and not just playback, definitely get an i5. If you don't, and your system is basically a playback/storage device, honestly you really don't need to spend the dough. Adding an SSD to your environment is an evolutionary leap in performance well beyond what even going up from a Core Duo to a Sandybridge or later I5 will get you. You can spend a hundred bucks and either get a dual core i3 if you don't have much use for multi-threading, or one of the AMD A8's if you do. Either option can get you a processor in the neighborhood of 3GHZ, that is radically faster per clock than Core 2 architecture, for under a hundred bucks.
If you do have use for the power of an i5 or better, they're fantastic hardware. I'd recommend you still drop 60 on a 120GB SSD though. That would give you enough room to be your primary OS and have some critical, frequently used programs on it. The advantage really can't be understated, something like a Samsung 840 Evo will have more of an impact on your performance than the rest of the system upgrade combined. Considering you should be able to more than double your performance with even a 3GHZ A8 or i3 build, that means something.