Both softwares are free (but not opensource). The only problem with "CDBurnerXP Pro" is that it does not work with files larger than 4.2 GB. So you cannot really burn a DVD images of say Etch distribution which are normally greater than 4.2 GB and less than 4.7 GB. However, "DeepBurner Free" has no such restriction.
According to http://www.cleansoftware.org/utility/#cddvd , "CDBurnerXP PRO" is also free from adware, spyware etc.,
PS: I was not able to find any free CD/DVD burning software for Windows XP, which has the facility to burn iso files and is released under GPL or is opensource. If you know of any, please let me know.