The Core Duo is 32-bit, the Core 2 Duo is 64-bit, which one of them do you have?
Both OSes should run fine, I would go with 7.

On the auctioning page was mentioned this one : Intel Core2Duo T7200 (2.0 GHz)

T2500 is "Yonah", a 32-bit CPU. T7200 is "Merom", a 64-bit CPU. (If the code names sound like Hebrew, it's because they are: these are the CPUs developed at the Haifa Design Center that turned Intel's CPU business around.)

Anyway, the V5200 GPU (it's the professional version of the X1600) is troublesome with Windows 7 and long since off AMD support.

This is an ideal platform for Windows XP; keep it on XP if you possibly can. (32-bit; don't screw around with XP 64).

Sorry those first specs were from a website, the second procesor is what I have in notebook. But anyway XP-32bit even for that other one?

The 64-bit version of 7 gives you the opportunity to run 64-bit applications, but at the cost of taking a bit more drive space (since it contains both 32-bit and 64-bit copies of a lot of libraries so that 32-bit applications will run). If you're not going to expand the RAM and/or HDD, I would go with the 32-bit version. I wouldn't choose XP either way.

64-bit is necessary to effectively use 4 GB RAM or more.

Yeah, 32-bit XP. Even if you have the 64-bit CPU, you don't have enough memory to make 64-bit worthwhile, and 64-bit XP is a strange OS with many compatibility issues. And getting the GPU to work with Vista or W7 would be a PITA anyway.

In that case, I agree with you, and change my previous statement. Choose XP.

Got it 32 bit xp it is then, thanks for your help :)

Bearing in mind a couple things:
* XP x64 bears the same version number as Server 2003, 5.2 rather than XP 32-bit's 5.1, and some installers simply detected the version number and thus complained "this is a server so I refuse to install".
* Hardware vendors hadn't yet fully hopped on the 64-bit driver train and at best had some unsupported beta driver (they hopped on the train when Vista was released, and seemed to begin to care about their XP x64 drivers about then as well).

...I really can't blame any of my issues with XP x64 on the OS itself.

XP 64 is indeed a crippled version of Server 2003, not the same thing as XP. That's what leads to the version number difference and the compatibility issues.

If you have an XP 64 setup that uses what amounts to server equipment (disks in RAID, lots of memory), you can do well with it. It's very good for nvRAID setups (nVidia's onboard RAID). If you try to hang a lot of consumer gear on it (sound cards, fancy graphics, USB webcams, things like that), it will be troublesome.

Anyway, it's way too bulky and has entirely the wrong feature set for a laptop.

I fully agree.

Then again, I knew quite a few people who used Server 2003 as a workstation and gaming machine, as I used XP x64.