Get yourself a good video card... (integrated graphics put alot of extra stress on your CPU, rather than that processing being done by a GPu on a video card).
You could also try firstly taking a backup of your assets.tdx file that's in your TRS2006 main directory, THEN DELETING IT. That way the next time you run Trainz it will rebuild your content assets data base... (the data base might be corrupt).
Cheers, Mac...