If the product key is there, you may use it with a 32 or 64 bit .iso (as the keys are interchangeable). Likely everything will be 64 bit compatible as the processor is 64 bit. Most likely it would of came with Vista Business Edition as it is a Latitude and they are Business models. Likely also 32 bit but as I said the keys are interchangeable and the hardware is 64 bit capable so that doesn't matter. It could of also came with Windows XP via downgrade rights. I fear that the COA might be faded given that it is on the base of the laptop and it is 4 year olds. You will need to verify with the user if the product key is readable. If it is unreadable the retail .isos are useless. I would need the actual eBay link to investigate further. As a side note your Dell Windows Vista 64 bit Ultimate reinstallation disc will work with the system via the Dell SLP however you will be incorrectly licensed if the COA is not for Ultimate. 
Hi, Looking @ a Latitude D630 on eBay that has no OS.  From a picture of the label I can see the Service Tag & the seller has Windows Vista in the product description.   Since 64-bit chipset  I need to figure out what was on this PC when sold. I have checked the original system configuration & manuals on the Dell website for this service tag but cannot determine what version of Vista.   Is it possible it came with 64-bit Ultimate?  Just happen to have a re-install disc for that.  Did find this site to download .iso re-install from Digital River but will still need to know 32 .vs 64-bit. [URL]  How can I tell which Vista version was originally installed on this D630?  Without contacting seller.  Here's some info you probably don't want. Specifications: [URL]#wp1105750 Intel® Core™2 Duo Processor T7300 (4M Cache, 2.00 GHz, 800 MHz FSB) [URL]  thanks   
Latitude D630 on eBay but cannot tell which version of Vista, 32 .vs 64-bit