Just buy an Aspire One with Windows XP installed - it will be less expensive that way.

Good Luck

I will change the os new os install in xp

Wiping a pre-installed OS sounds really quite dodgy to me. It's much easier to install Xp as part of a dual-boot setup
https://help.ubuntu.com/community/WindowsDualBoot

Sorry, this guide does specify that it's for Ubuntu but all the various different linux versions (we call them distros) work in very much the same way so it should help.

As you say the main problem is the lack of access to a cd/dvd-drive but it might be possible to either hire/borrow/acquire/buy an external cd/dvd-drive or alternatively get a lead that can plug into a normal drive and then into the Usb2.0 socket at the back of the laptop. This 2nd route would be the most versatile since a £10 (appox) lead then gives you options such as using a hard-drive as an external hard-drive as well as the solving the current problem. I got one for about £5 but it doen't include a power line so i have to sort that out separately.

Alternatively there is probably some way to install Windows over a network link but that's a lot more difficult to do with Windows than linux and i wouldn't have a clue how to start going about that. It's worth hunting around for a guide on HowTo do that.

It occurs to me to wonder why not just try linux? Give it a fair go and you'll probably find it a lot easier than people make out. A lot of the troubles people have is with installing it rather than using it - and with it being pre-installed you don't have to worry about that. Given that linux is exponentially creeping into the desktop market and already has the server and other markets i think it's safe to say that you are going to see linux around much more as time goes by. There are also a lot of guides around such as this
https://help.ubuntu.com/community/SwitchingToUbuntu/FromWind­ows
http://wiki.linuxquestions.org/wiki/Linux_software_equivalen­t_to_Windows_software

As well as plenty of help available such as in this general linux forum
http://www.linuxquestions.org
they might give quick incomprehensible answers at first but people tend to be quite happy to explain detail or help guide you through. It's not like the old days and i haven't seen anyone dare to try "Rtfm" or anything like that for fear of being kicked out of 'their' forum ;) Nowadays there's a lot more of us and some of us noob's are a lot less unfriendly than the old reputation :)

One reason for giving linux a fair go is almost total absence of any need to worry about security issues. It's so solidly written that linux malware is an endangered species
https://help.ubuntu.com/community/Antivirus
http://librenix.com/?inode=21

Anyway. good luck and regards from
Tom :)