By combining do you mean you have several tables with the same exact fields, but different data? If so, use append queries to move the data between the tables.
If you are saying you want to combine several tables that have different or extra fields, then you should double check your structure to make sure that you are not denormalizing (although for some RARE instances denormalizing is ok) your tables. If you aren't sure about normalization, do a search on the forums here as there are many, many, many posts about it. If you go into the Advanced Search feature you can even search by poster, and I would put in Pat Hartman as the poster if you want some really good information.