"Some Americans may have sent video home movies to a European relative, only to discover that the images are scrambled and the sound quality is very poor. This is caused by a major difference in broadcast formats used by the United States and many other countries. The United States favors a format called NTSC, which is short for National Television Standards Committee, while Europe, Australia and parts of Asia use a competing format called PAL, or Phase Alternating Line."
"Another difference between NTSC and PAL formats is resolution quality. PAL may have fewer frames per second, but it also has more lines than NTSC. PAL television broadcasts contain 625 lines of resolution, compared to NTSC's 525. More lines usually means more visual information, which equals better picture quality and resolution. Whenever an NTSC videotape is converted to PAL, black bars are often used to compensate for the smaller screen aspect, much like letterboxing for widescreen movies. "
"For most purposes, the difference between NTSC and PAL signals are negligible. A European television set won't work in the United States and an NTSC formatted DVD won't play on a PAL player. But many people own home movies which cannot be viewed on a competing format. For this reason, there are a number of companies which offer conversion kits from NTSC to PAL or PAL to NTSC. Some of these conversion methods can be time-consuming and variable in quality, but others provide an easy way to create a PAL video for a European relative or an NTSC DVD for a Canadian friend. Some electronic media outlets may also provide conversion services for a price."
So knowing this you will loose some quality in the conversion. As mentioned by the above quotes going one way or another isn't equal to quality out.