I will go out on a limb and assume you have already looked into the sticky for conversions which lists several first and second edition conversions. More importantly, what you will need to decide is if you want a direct conversion that you can share with the public, such as in the sticky for conversions (we will all appreciate the work and you can get some help here on the boards) or if you will want the adventure to "make sense" as it did in the edition you are converting from (some direct conversions will have some wacky results of too easy or insanely hard for the recommended levels). If you go with the first route, you will only be able to use material from the three core rulebooks (or any rule sets not considered an optional rulebook) and you will not be able to "adjust" any hard stats to make anything fit better for the recommended level of the adventure. If you go with the second route, you will not be able to share your conversion publicly, such as on these boards. These are the primary reasons why many conversion projects are abandoned as they cannot be shared or are too wacky to make sense.
As mentioned in a previous post, there was a small pamphlette published at the beginning of the third edition to assist people with making conversions (I am sure it is still available as a free download from WOTC). It contains broad generalisms, but is not a hard and fast item for some elements. Obviously, those elements that did not exist in the second editon and intruduced during the third, such as feats, have nothing to convert. These are the areas you will have some free reign to push the conversion in the direction you desire. Also, there are a couple of third party monster books you can draw ideas from for conversion of monsters that do not appear in the monster manual (such as the Tome of Horrors, hint hint).
