Fitracer computer control mod

[rmglb]

I've got a 'Fitracer' (quite similar to the Bit Char-G afaik) for quite some time now. And started hooking the controller up to the parallel port of my computer.

The controller works by grounding leads to the chip when pressing a (direction) button.
I hooked it up (ugly) by soldering wires directly onto the PCB, to the buttons/chip. When inactive i set all bits high, so they are at 5volt (from computer, which is higher than the normal 2AA +/- 3Volt). And when active its' grounded. (Ground of parallel port is connected to controller ground).

It used to work qutie well until i soldered things. Sometimes I can drive the car all directions, but often only in afew directions (most of the times i have to steer to let it drive).
I also didn't want to use batteries anymore, but take power from my pc. I'm using the 5Volt line of a PS@ (mouse) connector. I read an article of someone making a plane based on a miniRC and he wrote that the chip should work on 5V or less. He used a 9V block himself so added some more components to get this voltage down.
Here my charge led starts to light up when i simulate buttonpresses, and it doesn't stop anymore. So I'm probably doing something wrong here ;P

*** The controller can work on 5Volt right?

Also charging now isn't that wise.. a transitor and resistor (in the controller) are getting very hot (even at start) and the charge led won't go off anymore. I think the car used to take a current of 0.5A from the batteries when charging. But it's about 1A now when using 5Volt from the computer.
I always thought the controller had some elctronics to measure how much the battery in the car was charged. Since measuring the voltage on the 2 charging leads showed a rising voltage till 2V and then it would stop. But now i understand that that's probably when a capacitor is full, or something.

I'd like to charge the car based on the 5V power supply, but i have to find out how to do this. My car isn't modded and has a normal 1.2V 60MA battery.
*** Any tips on how to do this?

Also i can control my car remotely using a Java Applet (grabbing keypresses) and a webcam stream. But for this i will have to make a docking station where i can charge my car. I've got some ideas for that. But what's the problem is that I can't keep running the car until the battery is empty, since then I can't drive it back to the docking station anymore.
So I'll probably overload the battery eventually, or not?

*** Any ideas about this?

Thansk for your hints/ideas/tips.