- Windows 7 does not come for free and Microsoft no longer sells 7.
And there is no where safe we can recommend to buy it from.
- XP > 7 was done by a clean install.
- Dell does not support or supply Windows 7 drivers for your model number.
In fact Dell brought out a lot of machines in XP days that were solely for use with the XP operating system. https://www.dell.com/support/home/en-au/product-support/product/inspiron-6000/drivers
- XP is unsupported and so is Windows 7.
Warning:
You do not buy a Product Key by itself, as they are normally stolen/pirated, Volume Licenses which are not for private use, or MSDN keys which are not to be sold by the original subscription holder.
Make sure that you buy the complete sealed package (DVD, license)
https://www.microsoft.com/en-us/howtotell/Shop.aspx
Read Section: Beware of Product Keys sold separately.