Translation:I saw him yesterday.
In English, using a comma in this way is a topicalization of what comes before it, which is the same function as is expressed in Japanese by the use of は. I don't think using a comma this way in Japanese is generally equivalent to using は, even if it seems to be so for (some set of) time expressions. Hopefully, someone more experienced will be able to tell us.
In romaji (roman characters) 見ました is written as mimashita. But the i in mi is pronounced like the i in ski - this is probably why it sounds like me (in English) to you. In Japanese the e sound is pronounced like the e in get. Here are the Japanese vowel sounds for anyone else who is wondering - there are only 5 and they are always pronounced this way - same vowel pronounciation as Spanish, Maori, Samoan (and other polynesian languages) etc: A is pronounced like the a in Father i is pronounced like the i in ski u is pronounced like the u in fu of kung fu e is pronounced like the e in get o is pronounced like the o in got
I guess it would depend on how you pronounce that sound where ever it is that you live. For me the a sound in father is like the sound you might make if startled Ahhhh!! or upon discovering something - Ahaaaa!! and the o sound in got is a short o sound. They are not the same at all. The Japanese o sound is not the same as the o sound in hello or hope at all. Anyone who has taught you this is wrong. For me the o sound in hello and hope is the same as the oe sound in toe. Then again it might just be a different way of pronouncing vowels due to location, accent, dialect etc. At any rate the vowel sounds in Japanese are the same as for Spanish or for any Polynesian language.
LordOfTheAndain - I think it also depends on where you live and your resultant accent. The same English words can be pronounced very differently depending on where you live - country to country and even different regions and areas in the same country. Think Flight of the Conchords where Brett tries to tell people his name and they think he is saying "Brit". The 'o' sound in Japanese is a short vowel sound like in the o at the start of the word Octopus.
I'm not really sure about your exemples. In french, we have two ways to pronounce 'o' : one we call 'open o' which sounds like 'got', 'god', 'power'... And one we call 'closed o' which sounds more like 'call', 'boat' or 'toe'. I'm pretty sure the japanese 'o' is a closed one...
Actually, it's a mid back rounded vowel, so it's inbetween the open o (IPA [ɔ]) and the closed (IPA [o]). According to Wikipedia, it is close to the older RP pronounciation of "got", but RP has shifted towards a more open pronounciation during the 20th century so today better words might be those with long vowels such as "north" and "thought" (or indeed "call"). And in other varieties than RP other words might be better comparisons, but "hello" and "hope" generally have diphtongs, which is definitely incorrect.