As far as I know no one is offering a downgrade option but some manufacturers are now offering choice on a new computer purchased online such as Dell and Gateway. You can use the upgrade version of XP if - you have a previous version of Windows - Me or 98, during install it will ask you for the CD to verify you have a previous version, your only problem may be if the laptop has a SATA drive, XP will not see it for installing so you will need to disable this feature in BOIS if it is there, since nothing comes with a floppy drive any more getting the drivers on during install can be a chore. The other down side is hunting down XP drivers for the hard ware on the computer, video, LAN, modem, sound as XP may have the generic versions of some of them but you won't have full use of the features. It must be an XP CD that is not installed on any other computer, it can't be an OEM CD from another computer. Other then open source software I do not know of any software maker that allows you to use one copy on more then two computers - usually a laptop and a main computer are allowed.
As for the defrag program I have used this one and it seems to do the job and is free: http://www.iobit.com/iobitsmartdefrag.html I have never been a fan of Windows defrag as it is slow and frankly I don't take the time and never do it. Since I test software, a lot is beta, for allot of people before I recommend it to them I do allot of install and uninstall so for me I also run a reg cleaner now and then and usually every year or so I do a complete format and install to start over again so it's like getting a new computer.
I purchased "good deal" Vista computer and put over 30 children's games on it ranging from old 95 to this year, what I did with the older programs that didn't want to install, is open the CD and right click on the installer and choose 95/98 compatibility, close that down and double click on the installer and they installed and run fine on Vista, I had problems with this in XP. I am down to one old version of Motorcycle Madness that will not run correctly but it did not run great on XP either.
My thought is if I got a computer for around $300 it would not be a deal if I had to also purchase XP for it - ram is given since even on inexpensive XP machines when it first came out, I have purchased that and now it is at a low so for $24-44 on sale, I upgrade that, where XP with Service Pack 2 has a sweet spot of at least 512RAM I would say Vista is 1GIG. Since we are not serious gamers this has always worked for me.
I purchased a mid priced computer with Vista on it the day it came out I have been able to do pretty much everything I need to do on it, since then I have purchased a laptop and another computer with it on it. I did actually purchase the XP upgrade for my main computer when Nero, my U3 flash drive and HP all in one didn't work as expected and then decided to switch between the two with dual boot, now for the past month I have been in Vista only, I can do with out Nero, the all in one has HP supplied generic drivers which they gave MS and I didn't use the U3 program past using it to safely eject the drive.
My only grip is wasting horse power on an operating system when I would rather use it for the programs I run on the computer, I have found some computers deal with Vista fine and actually do better where others are just a dog with it on there no matter what you do, I do allot of tweaks on the operating system as I run programs on my computers not look at the eye candy of the operating system hence I have no need for Areo or slide in and out stuff - all that gets turned off - I like nice wallpaper that's it. I turn off User Account Control as I haven't had that for 12 years I don't need it now.
What I do find amusing is how people bashed XP and now it's the best thing since the wheel. This entire thing has been a win win situation for vendors, some people are buying new hardware to conform, some are buying XP to go back and then some are just coping and dealing and are able to move on with Vista with out much ado. I have gone from Windows 3 to 95, 95 to 98, 98 to Me, XP was the biggest jump and caused a stir, now Vista is the same hub bub but more people have computers and actually use them so the roar is louder. Not much of my current software would run on the old Pentium 166MHz I have here so we have progressed and paid for it each time.
Hope this helps,
Northlite