Need to buy for a clean install on a new HD on my S-I-L's old HP Pavilion 753n rig. It came with Win 7 Home Edition. HD is failing and was too late to image. Macrium Reflect gave it the good ole college try but it would not work. I assume the 753n can handle SP1 but I do not know pros/cons or if it even matters? Thanks.  If you are doing a clean install on the same PC and you have the COA code no need to buy Win7 again...
You can DLoad a version from Digital RIVER and use your liscense key to activate...
Completely legit to do so.P.S. the Editions have to match...As patio SAID, as long as you have a valid licence and key you can just download the media to install it - http://forums.mydigitallife.info/threads/14709-Windows-7-Digital-River-direct-links-Multiple-Languages-X86-amp-X64/page59?p=470600&viewfull=1#post470600

That said, I would never CONSIDER buying a new copy of Windows 7 for that machine, you would be looking at spending $100 on Windows after already spending $60 on a hard drive, this is simply not at all worth it for a machine that old.  There is a time when a PC is simply too old that you start wasting money trying to keep it going, For $160 you could easily find a second hand PC that would be much newer and more powerful.  I felt that $60 for the hard drive was already more than the machine was worth, throwing another $100 at it would be silly.

To answer your original question, like any Windows update you should have SP1 installed as it provides a lot of security and other patches to the OS.Thanks Cameronguy but my S-I-L wants this machine fixed up, no if's and's or but's. Quote from: patio on August 09, 2014, 10:46:33 AM

If you are doing a clean install on the same PC and you have the COA code no need to buy Win7 again...
You can DLoad a version from Digital River and use your liscense key to activate...
Completely legit to do so.

Thanks Cameronguy but my S-I-L wants this machine fixed up, no if's and's or but's.

It would be stuck on the tower on a sticker or in a box with the DVD which you don't have, this is of course assuming the original copy was genuine.
Just ensure she does realise that she could easily get a much better machine for the same if not less money, a lot of people don't realise this and think that fixing their existing one will work out cheaper.

P.S. the Editions have to match...

Where could she get a much better machine for $60 or less?

Ok, now I will show you how computer dumb I am. How can I download Win 7 onto a new hard drive? I will not have a browser to connect to the internet. Do I have to download it to a different external storage device? How do I then get it onto the new hard drive? Thanks.