which windows is better for my mbp mid 2010?

hey guys
i need to use office apps and i won't pay to app store so much money. I'm using macbook pro mid 2010, 2.4ghz intel c2d, 6gb ram, 5200rpm hdd.
i tried before to use with windows7 and it was runs hard.
So, should i continue with w7 or i must try earlier windows os? İf i must try earlier os, how can i install it?, bootcamp allows only w7.

I'm not quite clear on your question, but you can certainly buy and use the Mac version of Microsoft Office. In my opinion, the latest version is the best one they've done in years for the Mac, and is available either as a subscription (US$7 a month) or outright purchase (US$200). There's no particular reason to run the Windows version unless you are using some obscure features that aren't in the Mac version.

If you simply need a word processor that offers Office compatibility, every Mac word processor has that, from TextEdit (free) to Pages ($20) and everything in-between.

If you need a free alternative to the entire Office suite, take a look at LibreOffice or OpenOffice.

İm sorry for my English. So, just I will know which Windows will work probably on my Mac?

If you're using Boot Camp, then you'll want the version of Windows allowed by the version of Boot Camp you're using; there's not really much choice. On an older machine like a 2010, I'd suggest sticking with Windows 7, as anything older than that is very insecure.

If you prefer to run a virtualization program such as Parallels, you can run any version of Window you like. Again, however, there are some security concerns about older versions, and some system requirement concerns about the latest version given the age of your machine. Others will likely chime in with what versions of Windows they are running on their similarly-aged machines.

So, I will use bootcamp and i will install w7. Thank you so much for your help