which country are you in? in the uk the only one i have found without the os is ebuyer-- at the moment they only have 2 models available and the one with the sis chipsets not suitable for linux due to no graphics driver--but the models available change all the time next week they may have 8 models available
no guarantee how well ubuntu will go on any pc --if you are not used to linux and the wireless or graphics driver for example wont work its much harder than windows to install a driver--its not a case of download and double click the driver to install it you will need to command prompt the install
by default it wont even let you log in as root (administrator) so you have to su (switch user) to root to get temporary root priviliges this can get really annoying every time you want to do stuff--you can get round it though to allow permanent root log in--not knocking ubuntu i have all my machines on dual boot with ubuntu and windows and its a great linux distro but its a steep learning curve if things dont work out of the box
Try Avadirect, they do pre-installs of ubuntu (or leave it blank). Or RJtech, they won't preinstall ubuntu, but they give you the option to leave it blank.
Ubuntu has several generic drvers that allow it to run on a majority of hardware, but no guarentees