MD5->PHP how?

Hi, I am trying to work with 2checkouts MD5 HASH to make a client that will confirm that the order did actually come from 2checkout. I have never worked with MD5 and after 2 hours of reading am as confused as when i started. On the 2checkout site they have given an example in perl http://www.2checkout.com/md5_specs.htm Which I will copy the main part below: ************************Start copy*********************** The MD5 Hash is generated using the following values in order: 1.. A Secret Word value known only to the seller and 2CheckOut. (secret word now is "tango") 2.. Your Seller Number (my seller number: 12324) 3.. Total Order Number ( Including Seller Number , i.e. 123-12324 ), 4.. Amount of the Sale ( no currency sign or commas ). Note: The whole MD5 pasback string will be converted to UPPER CASE. ************************End Copy************************* After 2 hours of reading (www.faqs.com/rfcs/rfc1321.html), the manual etc I have found I will most probably need the md5() (string) function or "mcrypt" to do this...but am still totally confused. Any and all help appreciated, be it in comments,suggestions or anything. If possible please send me some code with regards to the above as I think if you just explain it to me I wont get it because so far I have tried by reading the RFCs, the manual and what not on my pal....google. :-) Thanks in advance. Cheers, -Ryan