No, that is not possible. Windows RT means it is running on mobile hardware like phones (ARM processors). Windows XP runs on x86 processors (Intel and AMD) so it will not be possible to run Windows XP on a Windows RT device. However, the Surface Pro and other Windows 8 tables (not Windows RT) will be able to run software that was able to run in Windows XP.
You just need to look at Windows 8 tablets (Microsoft's version is called the Surface Pro but others will make them as well) and not Windows RT.
That is correct. Theoretically the only Windows applications RT will be able to run is Windows 8 ported over apps. The way Windows 8 was designed should make it easy to make things also work on RT but anything that was pre Windows 8 will not. Of course there may be exceptions and some developers may choose to make older things work on Windows RT but the amount of effort to do that makes it very unlikely especially when anybody who needs that kind of legacy support can simply opt for the full Windows 8 tablets instead of RT.