Kwasniewski was the architect of the post-communist movement along with Miller. Together they forced the 'beton' (cement - apparatchik class) to understand that it was change or die in the fall of 1989 and the first half of 1990. They also systematically shut out the genuine reformers - those who wanted to create a new left wing party rejecting the traditions of the PZPR in favour of those of the PPS (Polish Socialist Party) and European social democracy. It is very difficult to separate out Miller and Kwasniewski during this formational phase. The new party was devoted to preserving as much power and wealth as possible with little if anything in the way of a real ideology. The SLD first came to power in 1993 with Kwasniewski as the power behind the throne as several PM's came and went. That government instituted corruption and patronage on a massive scale, particularly within the state-owned sector. As president (starting in 1995) Kwasniewski has generally done his job well, but with no discernable ideology beyond a generalized attempt to advance Polish national interests and, when he can, those of the post-communists. During the past four years he has also fought with Miller's faction over control over the SLD. As far as personal corruption goes, relatively little (by Polish standards) - just various family members getting lucrative 'consulting' contracts. He did, however, play a key role in institutionalizing the patronage and kickback nature of the SLD in its early years. His style is that of the youthful technocrat rising above the division of communist/anti-communist.

On the other question - I believe that the existence of so many active oppositionists made it both unnecessary and difficult for Party members to get into the non-SLD. There were literally thousands of full time anti-communist activists tied together by both fervent opposition to the system and tight knit social connections. Tens of thousands more (at least) were part-time activists, ten million adults had been members of Solidarity. In those circumstances the taboo against accepting ex-communists was able to be maintained. Hungary never had the sort of comprehensive mass movement bureaucracy that Solidarity automatically created in every factory, university, and institute, down to the smallest towns. When that activist base was decapitated through mass internment in Dec. 1981 new activists immediately stepped up to work underground. These were people with hands on experience in grass roots organizing and political journalism, coming from every class in society with every possible political opinion from left wing socialist to far right.

The far right has plenty of people who worked with the regime, but for the most part they were not Party members. Rather they were members or associates of the PAX movement, a set of collaborationist Catholic organizations created in 1945 by the NKVD under Boleslaw Piasecki, founder and Leader of the ONR-Falanga (Radical-National Organization), the most extreme of Poland's fascist groupings in the thirties.  At lower levels some of the former ultra-nationalist Party propagandists work for them, but I don't know of any ex-Party types at the top levels of the extreme right.