hi everybody

i have a problem and i don't seem to be able to solve it.

the problem on a multiuser system how do i make sure that when i am 
saving records in multiple / single tables nobody else is writing onto 
the table/s at that time as i need to generate some numbers like, 
Invoice Number, etc. by code.  also i have to make sure that nobody is 
reading the tables that have the last generated numbers stored.

pls anybody help me as soon as poosible or i shall have to postpone my 
development till then.

thanks

bharat