Well, there's actually many ways you might account for this. Here's one way to do it:
First, set up an asset account to hold the T-Bill. You could set up a "brokerage" account called "T-Bills Direct" or something similar to hold this T-Bill, and any other T-Bills you might purchase. Record a transfer of the $4,950.65 from your bank into the new T-Bills Direct account.
Next, set up a "liability" account to hold the discount on the T-Bill. You could name this "T-Bills Discount" or something similar. Record an increase in this account in the amount of the discount ($5,000.00 - $4,950.65 = $49.35) with an offset to the T-Bills Direct account. The T-Bills Direct account will now have $5,000 "cash."
Next, buy your T-Bill in the T-Bills Direct account. If you think you'll only have one T-Bill open at any one time you could just buy a bond called "T-Bill." If you think you might have more than one T-Bill in your Treasury Direct account at any one time you might buy and bond called "T-Bill Due 3/30/2006" or some such to distinguish it from other T-Bill you might buy.
You'll now have a balance sheet with a T-Bill asset of $5,000 and a T-Bill "liability" (it's really a deferred revenue but Quicken doesn't have that sort of account) of $49.35 which nets to $4,950.65, which is just what got deducted from your bank account.
When the T-Bill matures you "sell" the T-Bill in the Treasury Direct account for $5,000 (no capital gain or loss) and transfer the money to your bank account, which is just what the Treasury will wire into your bank. You then go over to your T-Bills Discount account and reduce it by $49.35 (bringing the account balance to $0) with the offset being something like "Interest Income:T-Bills." You now have nothing on your balance sheet for the T-Bill except the $5,000 in the bank, which is correct.
The above treatment isn't theoretically "pure" - you should really accrete the discount to income over time - but, since T-Bill interest isn't taxable until the T-Bill matures the above method is consistent with tax purposes.
Tom Young