I can vouch for the translation: "colgate" here means "hang yourself" or "hang you". Notice that this differs from "normal" Spanish (Spain and most Latin America), because our "voseo" (for familiar second person speaking) alters grammar -in Spain it would be "cuélgate".
This matches the testimony here.
It must have been surely an unfortunate coincidence for the marketers, but I don't believe that it was a great deal; people just understand and get over it. And I don't think that the coincidence is so terrible as it might sound. First, we don't normally use that word to as a colloquial insult or curse, as in English - Spanish speakers might say instead: 'matate' (kill yourself) o 'pegate un tiro' (fire yourself). Furthermore, the verb "colgar" has quite other meanings, apart from the act of killing hanging from a rope. For example, currently, it's also used as younger slang for "to take part of something" (similar to "hang out") and there are more related "positive" meanings.
There has been some much more unfortunate coincidences: the Mitsubishi Pajero had to be changed (to Montero) because pajero is a very strong and vulgar word in many Spanish-speaking regions (wanker).
Update: an interesting point is raised in the comments, regarding the pronunciation. We (I'm speaking about Argentina, and most non-English-speaking countries) are used to pronounce most "foreign" words not by following the Spanish phonetic rules, but with the original sounds (well... approximately). Say, we pronounce "Seven Up" as if the last syllable had a Spanish 'a'. But a word like 'Colgate' can make us hesitate, because it feels like a Spanish word, but we (might) know that it's foreign. And, indeed, a few people here pronounce 'colgueit', ala English. A consensus is normally formed, often driven by TV-radio announcements. Hence (and this is the point of this disgression) one might guess that the marketing should have try to impose the 'foreign' pronounciation in the announcements, to dispell the unfortunate coincidence with the Spanish verb. However, for some reason, that didn't happen (because the Spanish pronounciation was already established, or because the coincidence didn't matter? I'd bet for the later, but that's just my guess). See for example here (Mexico, ~1960) and here (Argentina, ~2010). The same happens in Italy.