if you're talking about making linked text in a text field change colour onRollOver, it's pretty much not possible.. if all you want to do is make a button out of text, try this:
grab your text tool (T)
type out what you want your button to say
select your arrow tool (V) - your text should automatically be selected. if it's not, select it.
convert it to a symbol (F8 or Insert>>Convert to symbol)
choose button and call it whatever you want
double click into your text (which is now a button) - you'll see one layer and 1 keyframe (with over, out, down and hit frames)
Select your text frame and add three keyframes (F6 thrice or Insert>>Keyframe) you should have your text in all four frames now.
Select the second frame and select your text. In your properties panel change the colour of your text. this will be the over state.
Select the third frame and change the colour of your text to whatever you want your down state to be.
in the fourth frame, get your rectangle tool and draw a rectangle around your text. This will determine the "hit area" of your button. in other words, where the mouse has to be in order to trigger the over and down states. Once you have your rectangle, you can delete the text on the fourth frame.
Test your movie (CTRL-ENTER) and when you roll over and press your text you should see it change colour. To make this go to a url, make sure you're on your main timeline, select your text button and put the following script in your actions (to pull up the actions panel, hit F9). To make it so you can type stuff in manaully, hit CTRL+SHIFT+E (for expert mode):
This is the most simple way to make a button
try consulting the flash help for different methods/ideas.