You should carefully research this before doing anything. It is very difficult, indeed, with a lot of paperwork and a long waiting period. By far the easiest method is through the K-1 (fiancee) visa. If you instead marry someone in the DR and then try to get a visa, it will take at the very least 1 year for that visa to go through.
The fiancee visa is usually faster than that, but there are no guarantees.
The process is for fiancee visa is straightforward, though at times convoluted:
1) you file a form and some documents with your local INS district office
2) they send you confirmation that it has been approved
3) your file is sent to the US consulate in Santo Domingo to be evaluated. The INS in the US does not make final determination on the issuance of visas, only the US Consulate does.
4) the consulate mails you a packet of forms to complete
5) you are scheduled for an interview at the US consulate where the American fiancee MUST be present
6) if you pass their tests, your fiancee is granted a temporary visa
7) once fiancee arrives in US you have 90 days to marry and file for a "change of status" to permanent resident
8) you must remain married for 2 years and usually pass another interview at your local INS office in the US before a permanent residency is established.
Good luck
