I want to install Ubuntu using the Windows installer on my old HP running Windows XP. If I do not delete XP (so I have to choose what OS I want each time I boot), will all the files and programs on XP be deleted? If not will I be able to access them through Ubuntu or will I have to load up XP to get at them?
First of all, let me clear up some confusion you seem to have. If you use the Windows installer (Wubi), Ubuntu will be installed inside Windows onto a virtual disk (not partition) and will be thus vulnerable to Windows Filesystem Fragmentation and other issues. This option does not put your files at risk on Windows (though it does put Ubuntu at risk).
Ubuntu does best if you install it on its own partition, and you can use the Ubuntu installer to do this. Once installed, Ubuntu can access your Windows files (which will be on another partition). In fact, it can even do this when running as a LiveCD/USB. If you use the advanced partitioning options, you can even have your Windows partition show up as a folder on Ubuntu (such as
If, by "windows installer", you mean to say you want to install Ubuntu "inside" Windows, then no files will be deleted and you will be able to access your files and folders even in Ubuntu. However, you won't be able to run your windows applications directly in Ubuntu. You can run some of those, if not all, using applications like wine.
All files which are stored in the virtual disk where Ubuntu is installed are stored in a folder
For more information, read this. If you have trouble installing Ubuntu, please refer to the above link or you can also post your queries or problems here, if they are not already posted.