Tables > 255 Items?

I've been running into this problem in Access. I have records which have more than 255 fields. The easiest solution would have been to get a table with more than 255 fields, but I can't do this, so I've had to split up the tables. The next easiest solution would be if there is a way to link the tables--I have a data field "IntAccNum" identified as the primary key in each table--so that when a new row is formed in one, it is formed in the others. This wouldn't waste space, since any row in the first table would necessarily need a corresponding row in other tables. Is there a way to do this?

If not...

The problem I run into is when I populate a row in the demographic table and then try to fill a corresponding row in another table. I use a command button to for a macro to "OpenForm", and then try to "SetValue" of the appropriate field in the second table. This adds a new row in the second table. This does let me populate the correct row of the second table the first time I try for each row. However, after this initial population, when I switch back and forth between the first and second table, I get an error in access since obviously I can't keep adding a primary key with the same value in the second table.

Do I need to do some sort of query to see if that row exists in the second table already. Or is there some simple solution to what must be a very common situation that I am overlooking?