Well, yeah, there is a catch. To read and process the serial data from the GPS with your own code and not use the library functions you need to understand how the serial comms work. It is asynchronous which means there is no coordination b/w the sending device and the receiving device.
The Arduino serial buffer is just 50 bytes (or is it 64?). When it is full nothing tells the GPS to pause, so data is lost. You have to ensure your code reads all the data and processes it and does what you want to do in each cycle without allowing buffer overflow. Read Robin2's helpful tutorial on serial comms:
If you increase the GPS baud rate it may become too fast for your code to get it all. You end up with corrupted sentences.
I would start wth 1Hz and 9600 baud. Get that working and then try increasing the output frequency and baud rate incrementally.
Do you actually have a GPS module at this stage? Are you using it with u-center?