Vostro 3400 with Windows 7 64

The 3400 can be configured with either 32-bit or 64-bit Windows 7.  Often businesses will order 32-bit for potential compatability reasons with legacy, proprietary, and often very expensive software, but 64-bit can be configured at the time of order or installed after the fact, as Dell does have drivers for it.  A direct upgrade from 32-bit to 64-bit is not possible ... you would need to to a clean/full install of 64-bit.  Whether or not you can manage that without paying for it is another story.  The Product Key on your computer will work for either version, but Dell will not send you the 64-bit disks if you ordered it with 32-bit.  Your best bet ... return it and order it with the OS that you need.  Alternatively, if you have a 64-bit installation DVD that came with another machine, you can use it to install on your 3400 without violating any licensing.

There are, however, very few programs that will not work with the 64-bit version of Window 7* - most of them outdated/legacy/proprietary business software.

* There are of course applications that cannot run on Windows 7 at all, but what I'm talking about are incompatabilities because of the 32/64-bit question - there are very few.

I prefer to use 32 bit version of any kind of winodws. It supports all softwares very well without facing any problem. I think 32 version is better if youy don't have any special purpose which needs to be run on windows 64 bit.