how to create non-droplist categories

I would like to be able to use a text field to define a category similar to the "weight" category. How do I create my own category without using droplists?

The values of the categories are fixed, so they will always show-up as a drop down list. However in RQM 3.0.1 there's something new called custom attributes that are similar to categories except they are free formed fields, so you can enter what ever value you want.

Here's a link to the RQM 3.0.1 custom attribute doc:

http://publib.boulder.ibm.com/infocenter/clmhelp/v3r0m1/topic/com.ibm.rational.test.qm.doc/topics/c_create_custom_attributes.html