Hi Stikas,
If you downloaded the SAR 500 off the Download Station be aware that it was made for the first version of Trainz when our computers were less powerful than the Netbook computers you can now buy. As a result the model was designed with low poly and textures.
Also the sound files are for the original Trainz, to get decent sound in TS2010 you will have to replace them with sound files designed for TS2010.
The other problem is you will have to run TS2010 in compatibility mode, which may be why it is not visible in your rolling stock list.
Lindsay