Hardware (HW) mode means that your graphics card processes the graphics, freeing the CPU to do the rest. Software (SW) mode is used if your grahics card is not powerful enough to process the graphics, so your CPU must do all this work and the results are not as "pretty". To know what mode you are using, in the GP3 graphics options menu, check what render device is selected. You should see one of two choices: "Software" or the name of your graphics card (hardware).
Once you know this, you will know if you should download HW or SW tracks. Then make sure that you follow PRECISELY the installation procedure in the text file that is included with the track. The procedure can vary from one download to another.
Also, if you have GP3 v1.13 and you download a track or trackpack made for GP3-2000, the track might use some jams that are only included in GP3-2000 so there will be some missing textures.