taxing

I dont see the yellow line for taxi. I hace always to activate option that guides me to the runway,...help[/img]

Have you tried Airport Environment Upgrade v6.0 (aeu6.zip)
This freeware add on will

Airport Environment Upgrade 6.0 (AEU6) Will greatly enhance the Microsoft® Flight Simulator 2004 default airports throughout the world. Airport runway, taxiway, and tarmac surfaces, airport buildings, and airport lighting have all been upgraded. Special reflective windows and seasonal runway effects are included. This is the latest version of AEU as of March 14th 2004. The impact on performance has been addressed in this version, and was found to be an improvement over the previous release

From
http://library.avsim.net/search.php?SearchTerm=airport+upgrade&CatID=fs2004scen&Go=Search

Now I am able to see the taxiway clearly but I have problems staying on the line, my plane keeps going from side to side I have to hold breaks to line it.

What aircraft are you using?
Also if you are using a joystick try recalibrating it in settings

I know what you mean, my aircraft (Mainly the jets tho) do that too. It doesn't bug me all that much, just gently guide it back. besides, you know you shouldnt let go of the joystick untill autopilot has been engaged or you have trimmed the aircraft!

Same story but …exercising help a lot. The problem is that I usually rushing to take off

I also get exited befor the takeoff.

Take your time with takeoff. Make sure everything is in order and you feel comfortable before you run up the engines! It gets hectic, i know!