At 274 lbs (about 100 lbs. overweight), I found out I was pregnant last September. I am now the proud mommy of an 8 1/2 month old baby girl :)
My doctor told me (at 6 wks along) that I was destined to get pregnancy-induced hypertension and gestational diabetes. She wanted to schedule me for my c-section at that first appointment. I switched to a midwife and delivered my little girl naturally at the Allen Birthing Center this past May, and I had neither PIH or GD.
Yes, you are at risk because you are overweight, as was I, but it is not a certainty that you will have problems. I had virtually no problems throughout my pregnancy. You will have to work on your eating habits, as being sure to eat healthy is a good way to avoid problems. I would encourage you to check out the Brewer pregnancy diet, and to talk to your healthcare provider about a good diet for you (I don't mean diet as in to lose weight, I mean as in an eating plan). Everyone is different, but being overweight doesn't mean you can't have a healthy pregnancy. You can do it! :)
As for the morning sickness, I was just queasy a little bit for about 4 weeks, and then it was pretty much gone - but I think that eating little bits at a time really helped me through that. I've also heard wonders about preggie pops - you can order them online or you can get them at most maternity stores and babies R us.