Roll Call (big bucks subscription fee) reports Hastert will resign, “effective later this year”. The “highlights”…

Former Speaker Dennis Hastert (R-Ill.) is expected to announce Thursday that he is resigning his seat in Congress effective later this year, eventually setting up a special election to succeed him, knowledgeable GOP sources said late Wednesday.

Rumblings have persisted for months that Hastert, who announced this summer that he would not seek re-election in 2008, was unlikely to complete his current term.
[…]
One key issue for Republicans is the timing of a special election, which will be called by Illinois Gov. Rod Blagojevich (D), and whether it might be held in conjunction with the state’s Feb. 5 presidential and Congressional primaries.
[…]
The GOP would be slightly favored to hold the exurban Chicago seat in a regular election, but a special election could be problematic for the GOP because the Democratic Congressional Campaign Committee has far more money than the National Republican Congressional Committee.
[…]
According to state law, Blagojevich has five days from Hastert’s last day in office to schedule the special election, which must take place within 115 days.

Although the law is clear regarding when special elections must be held state law is vague regarding whether a special primary precede it.

Not sure what “later this year” means…but I’m not sure who will attend the pity party.