(MONEY Magazine) – Q. The trust accounts that my wife and I set up in our children's names have done well. According to the terms of the trust, the kids gain control of the money at 18. But we worry that fast cars may appeal to them more than college, so we plan to invest the trust money in a mortgage on our house. The kids' money will earn a fair rate of return, but their capital will be tied up until we pay off the mortgage. Can we do this? JYOTHI MANOHAR Rose Valley, Pa.

A. Yes, but it could be risky. Managing a trust for minors is a fiduciary responsibility with legal implications. No matter how careful you are to keep everything aboveboard, borrowing from your kids--which is what you would be doing--could expose you to conflict-of-interest charges, especially if the mortgage provides a lower rate of return than their accounts earned previously. Before proceeding, the question you may want to ask yourself is: Would my kids take me to court?

Q. For years I reinvested my stock dividends in more shares, but recently I sold all my holdings. Unfortunately, my brokerage can tell me only the total number of shares of each stock that I bought with dividends, not the cost basis of those shares. How do I calculate my capital gains? A. KHANIN Simi Valley, Calif.

A. There's no way around it. You must figure out what you paid for those dividend-purchased shares. Luckily, you sold all your holdings at once so it's not necessary to track individual purchases. Therefore, the only numbers you need are the cost of your original shares (including brokerage fees), plus your cumulative dividends for each stock. Add those figures, and you'll have the cost basis for your entire lot. Then subtract the cost basis from your selling price to get your capital gains.

If you didn't keep your statements and your broker can't tell you what dividends you earned, shareholder services or the transfer agents for the companies you invested in are almost certain to have records of your dividend payouts. If not, a good-faith effort to reconstruct your probable costs using historical data, which the companies will have, should satisfy the IRS.

Q. I know that after five years I can withdraw $10,000 (tax- and penalty-free) from my Roth IRA to buy my first house. But doesn't the law really allow me to withdraw more than that? DANIEL YAU San Jose, Calif.

A. Yes. In addition to the $10,000, you can always withdraw any Roth contributions, tax- and penalty-free. So if you put $2,000 a year into your Roth for five years and your account manages to earn an additional $10,000, you will be able to withdraw $20,000 for your home purchase. Your plan would be a tax-efficient way to save for a home purchase that's at least five years off, especially if you are already investing for retirement elsewhere.

Q. My wife wants me to get rid of my first computer, a Commodore 4032 PET. It still works great and, to me at least, has sentimental value. I hate the idea of junking it. Can you help me convince her that my old friend is a valuable collectible? JAY JAEGER Midland, Mich.

A. Sorry. Fellow PET lover Sam Ismail, who runs Silicon Valley's annual Vintage Computer Festival (scheduled for September; www.vintage.org), says he's never seen that Commodore model fetch more than $200. "There are just too many out there," he explains.

REPORTER ASSOCIATES: Jan Alexander and Adrienne Carter