What should I use for large 2d games

After having a quick look at your code I would say,

1.use Functions
especially for the bit that writes out 'blitz programmer'.

2.use XML for the map file format. do a search for blitz and XML to download the XML file reader that someone programmed.
also download microsofts XML file editor 'xml notepad'
3.use [codebox] instead of [code] on the forums