hi asterisk gurus
i need to know how many channels can use a single ivr file simultaneously
ie.capable of single ivr to be played in how many channels simultaneously
I think that this is more or less dependant on the hardware you are using to run your Asterisk server and some small performance tweaks (for example, having the IVR file in the RAM disk partition and so on). So if you want a clear answer, first define what hardware you are planning on using. Based on the current detail level of the request i can say - a lot of users can use a single ivr file simultaneously 
2X quad core xeon processor 4 gb ram
asterisk NOW is installed in that
I would suggest that you set up a test bed in the lab and simulate large ammounts of concurrent calls. You can monitor the load that the system is suffereing and then predict how many chanells a system can handle. I would say a lot more then a 1000, but it is very hard to say, because there a lot of things that can influence the results on such big loads.
But first, you definitly need to read some things about Asterisk and Linux performance boosting tricks. There is tons of literature online 