Um, I hate to say this, but I think you've missed the point behind an ESPP.
If the program at HP is anything like the one I had available to me at Apple, you sign up, some percentage of your salary goes into an account, and at the end of the ESPP period (typically one or two quarters of a year), the stock is purchased with your total contribution at 15% below the lowest price of the stock during the period.
So, you now own an appreciated asset worth at least
15% more than you paid for it. Possibly more, if the stock price increased over the period. The right thing to do is to sell it immediately
to lock in your gain, and then reinvest the proceeds (after taxes) in a diversified portfolio (e.g. a mutual fund or three, or five). Lather, rinse, repeat, every period. Main point: it doesn't matter one whit how well or poorly the company's stock is doing: you still get your 15%, at minimum.
Just to give you an idea of what a fantastic deal
this is, let's compare and contrast for a second:
If you didn't sign up for the ESPP and stuck that 1% of your salary in a savings account, you earn, what 2%? 3%? and that would be over the year,
not the half year or quarter year. You can do better in Treasury bills or Certificates of Deposit (CDs, about 3.47%), but again, over a year's time.
Taking that 1% and putting it mutual fund would do much better, depending on its composition; perhaps 10%, year over year, though you wouldn't be up all years. Long term, it's a pretty sure bet, but guaranteed
And yet the ESPP is still giving you 15% every three to six months!
The key concept is very simple: have your "spare" or "investable" money in the investments that are likely to return the most over the time the money is invested. The other thing is to control for risk: having all your money in one stock is asking for a world of hurt - it's better spread around.
An ESPP is not an instrument for investing in your company's stock. If you want to do that, buy the stock back again at market rates, after
you've taken your (minimum) 15% gain from the ESPP.