asp.net search application index update help

Question

hi

im developing a simple search application( ASP.Net VB.Net) the index table is actually a hash table ll be stored in my file system. the search page ll open this in read mode n copy this to a hash table object n perform search. other update n delete functions will open this in write mode n update it. what should i ve to do to make this app correct that there shud not be any execption when multiple user accessing these things at the same time. wat do i ve to do to make this robust and error free. i want multiple users to access search page without any problem n the index updation also in a parallel manner

thanks

srinivasan