I don't quite understand what happens if a stock you own is under a takeover bid. For instance, SAI is supposed to be under a takeover bid by Hong Kong-based Baring Asia Private Equity for $4.75.
At the time of the takeover bid, the following usually happens:
1) Company announces the bid to the market, with an estimated timeline. They will usually announce a per share.
2) Market participants usually buy the stock up to the level of the bid, give or take a few percentage points (if the bid is viewed as risky in any way, there might be a larger discount)
3) The company's board will give a recommendation
4) The company will arrange a meeting with shareholders to vote on the proposal
If it's approved:
1) The market is notified that it's approved, with the required effective date
2) Wait for conditions to be met, if required
3) On the date that it becomes effective, money is transfered from the buyer and distributed to each of the shareholders. This is done using the same mechanism (share registry) and money is transfered into each shareholders account electronically (or they're sent a cheque) for each of the shares they owned.
Probably some details I've missed, but that's pretty much it.