The Slavs migrated from the East in the 6th century to Slovakia, Poland, and that area. The Magyars migrated to Hungary around the late 9th century. Before this time, the people of those land masses spoke a different language all together.
I know that the Czech area was all Germanic with a tribe called Boii. However, I have no clue what the Hungarians were speaking prior to the 9th century.
Also, what were the Poles speaking prior to their Slavicization? My Polish friends were surprised that Slavic language was only introduced there in the 9th century AD.
For some reason, this topic is not given much attention in history books.
These questions are very complex ones, for various reasons. The first one is linked to the nature of sources. The only thing we have to probe into these areas at the periods you mention is a record of material culture, thanks to archaeology. However, modern research tends to be very pessimistic on the possibility to identify markers of ethnicity in archaeological finds. The second problem is that the farther back in time we are, the more likely it is that ethnonyms lose their meaning. “Hungarians” are a case in point: the Magyars have created what would become Hungary. The third one is that migrations are a hotly debated issue; for instance, various models exist for the Slavs, some of which heavily emphasise continuity of occupation.
That being said, I can try to tentatively answer some of your questions:
The area corresponding to modern Hungary was probably settled by some Slavic or Slavicised people. It must also be noted that modern Hungary roughly encompasses an ecological area called the Alföld, or the Great Hungarian Plain, which happens to be the westernmost extension of the central Asia steppe in Europe. Many nomadic people have therefore used this place as a base of operation; remnants of various nomadic confederations must have subsisted in the area. Most of them probably identified as “Avars”, one of the most impressive steppe powers of the Early Middle Ages (but they might have been assimilated in the Magyar army anyway, given the high degree of fluidity of identity in these nomadic confederations).
The “Poles” did not exist as such before Slavicisation, and depending on the truth we are prepared to put in the idea of migration, we might even think that the ancestors of the Poles arrived with the Slavic language. Anyway, the traditional reconstitution of migrations holds that Germanic people controlled a part of the Baltic shores before the Völkerwanderung (some of these peoples may be Goths, at least if we give credit to the connection between the Gutones of Pliny the Elder and “Goths”. Personally, I would contend that they are connected in terms of etymology, and that the latter Goths may have claimed a descent the former, but that we must be extremely wary of this kind of connections on the basis of ethnonyms. Examples abound of people claiming the name of a previous power without what we would consider to be a direct descent). Many Balts must have been there, especially in the East.
As a side note, I think that the Boii are a Celtic people — not a Germanic one. But the difference in border areas was probably not that straightfoward, and it is also probable that the area was partly Germanised in the Early Middle Ages.
The slavs never arrived from the east. They were in southeast poland and western Ukraine since the indo European times. All they did was move further north east south and west. So when you state them moving into europe like a fact that sounds agendaesce. Nothing is certain but now generally accepted that the north carpathians are the slavic families homelands. unlike the Celt and Germans the Romans never conquered the slavs and were not able to write and study them like they did in the west. Everything we know of Germans and celts back than is thanks to the Romans. Slavs are the largest ethnic-linguistic group in Europe. They didn't sprout from some insignificant swamp in the east if that's what some of you heinrichs are thinking.